@Marinera: Ya, he is the shit!
@Ironaddict: thanks man! It’s good to hear that people here are accepting of information coming from a member with less than 20 posts. ;) OK, I will attempt to answer your questions, but keep in mind, my PE experience is limited so this is strictly coming from my understanding of tissues - especially the collagenous connective variety - and how those tissues heal and lengthen.
The circulatory system: So the veins and other blood vessels in the penis should be addressed to improve the tone of their smooth muscle and increase bloodflow. If your penis gains size or elasticity you want to be able to fill that sucker with blood when it’s time to use it, right? Well, the best way I can see to do that so far in the world of PE, exercise-wise, are jelqs and jelq variations. Jelqing causes increased blood to be “shoved” through the circulatory system, conditioning it to handle increased bloodflow. The veins become used to carrying a larger volume of blood over time and the smooth muscle surrounding the vessels should improve in tone and the elasticity of the vessels should increase to reflect this. Now, you must be careful to not damage the vessels with overwork. Blood vessel (well really most kinds of tissue) damage usually results in scar tissue formation which causes hardening and stiffness - NOT a good thing in blood vessels! Their ability to dilate and contract is essential to their normal function and stiffening/hardening hampers this - as is the case with arteriosclerosis and the cause of many strokes. Not to mention, if you burst a blood vessel you gotta take some time off more than likely. Also, integral to increased bloodflow to the penis are..
The muscles of the pelvic girdle: These muscles should be strengthened as they work the valves controlling the inflow of blood into the corpus cavernosum thereby effecting stronger and longer lasting erections - taking advantage of the improved circulatory vessels you are building with jelqs, as well as a whole host of other sexually related benefits like increased stamina, stronger orgasms, higher velocity ejaculation (OH YEAH!), and have even been said to be the first stepping stone on the road to male dry/multiple orgasms. Kegels, kegel holds, reverse kegels, weighted kegels (with towels or weights hanging from the erect penis), anal clenches and reverse clenches, along with several other pelvic girdle muscle flexes and holds are the key exercises used to strengthen these muscles.
Managing soft tissue fatigue: Now this is not something you exercise for, rather it is something you need to keep a watch for as to not allow too much of it to happen as to not be able to recover adequately between PE sessions. The corpus cavernosum, corpus spongiosum, and the glans penis all contain soft tissue of different kinds that can be fatigued and damaged. Too much of this damage is problematic for a few reasons. First, if you overly damage these tissues, just like a broken blood vessel, you will have to take a while off. Second, extensive trauma to soft tissue will also result in the formation of scar tissue. A lot of scar tissue is never desirable in any tissue as it is hard and inflexible making gains harder to achieve, and really not great for anything functionality-wise. Signs of extensive tissue trauma such as bruising, spotting, or other discoloration over a large area of the penis or very deep in hue as well as subcutaneous bleeding, relatively intense or sharp pain, more than a minimal level of swelling that sticks around, and/or lasting coldness should all be watched for and a session should be immediately discontinued if any of these signs start to show in a way that has you even remotely worried. Sorry I cannot be more exact here, everyone’s tolerance/conditioning is different but it is always better to play it on the safe side. The problem with some soft tissue damage is that the signs will not show up until later. It is important, in these cases, that the trauma be allowed to heal - a break might be necessary for a couple days.
Pretty basic stuff you hear about a lot, but ANY program, be it hanging-, extender-, manual-, pumping-, or clamping-based needs to address the above factors and include/exclude the necessary components.