Privacy is an issue for a lot of guys here. I don’t have a problem so I can’t really comment.
You will find that these exercises become boring pretty quickly and control over your erection will become easier.
With stretches you’ll just have to wait for the erection to subside, maybe continue the hot wrap until they do.
What you are looking for when you are jelqing is matching the hardness of the grip with the erection level. Though you need to let a little blood through the grip you also need to trap quite a lot. You should feel stress above the point of the grip all the way up the stroke. There will also be increased stress toward the head but you need to try and even out the stress as much as possible with the tightness of your grip. With the correct tightness you will probably find that you will tend toward losing your erection more than anything.
The amount of time you take on each stroke is also important. Try to maintain a 3 second or more stroke time (count: 1 - one thousand - two - one thousand - three - one thousand). If your stroke is too quick or you speed up during your session your erection may rise.
When jelqing correctly you can expect to have a much increased flaccid size for some time after the exercise. If you don’t have this you may not be stressing the penis enough to see gains. That said be careful, if you overstress the penis (especially when starting these exercises) you can cause injury.
These exercises have worked for me. Its a long term commitment though you need to be putting in 1/2 hr a day or more for 1.5 years plus in most cases.
If you have already read the info above you will have many other examples of people who have gained.
Hope that helps.