Yes Qwerty, it is possible. The main drawback (excuse the pun ) is that you won't feel as much as you should. You also risk infection since you can't wash away the smegma but this risk is not as great as some people think. How are you going with the stretching exercises? The main difficulty with stretching exercises is that people sometimes don't actually do them. At your degree of tightness you should be pulling back far enough so that the stretched opening feels a bit uncomfortable but not actually painful. This exercise is probably easier with an erection but it's not essential. Hold that for a minute or two and repeat a few times. Do this on 2 or 3 occasions per day and you should see some improvement soon. I gather you have read the links I posted? Get back to us with any questions.
My first attempt at sex was with a condom on over a foreskin that wasn't pulled back (because I didn't know any better). It was less than successful because there was almost no sensation. So, the answer to your question is yes -- but!
If you are going to buy condoms you should buy the jelly at the same time. They are usually side by side on the shelf. The condom will prevent the foreskin being forced back but you probably won't feel much. Without a condom lack of lubrication is what might cause pain or you trying to thrust too strongly. If you don't want to buy lube then make sure she is very wet beforehand with lots of foreplay. Also use saliva on your penis and the opening of the vagina so that you are not thrusting into dryness. That's what's most likely to cause damage. Pulling your foreskin forward just before you enter may help too.