my take on this issue is that penetration is difficult due to the lady in question is not relaxed and or excited enough to accept the incoming object. the proposed remedy, using the foreskin as some sort of shoehorn might work technically, but is it enjoyable for both?
in my experience postponing penetration in favor of a long foreplay make a wold of difference. it enables the lady to physically prepare for the acceptance of the penis. her vagina will relax and widen and deepen from the normal state into the welcoming state. at the same time her glands will start to secrete enough moisture to accommodate a smooth glide/ride. this combination will accept any penis though gentleness is of course the key. moisten the bare glans first by rubbing gently it gently between her inner lips, then slowly and gently push the head forward not more than half of it. repeat the above and gently push the head further into her vagina. no pressure or force. only when you achieved full penetration - that also depends on the lady's preferences. some like an as deep as possible others like a more half-way approach. remember, only the first few centimeters of the vagina are very sensitive, further 'up' the sensitivity is less. when the desired depth and smoothness is reached, you can thrust a little harder and if so desired faster.
of course the position taken to do the deed is affecting the result. some positions cause a tighter grip while other offer more room to move. most important is to talk about what you and she feels during the activities. be open to each other - sex is a pleasure not a chore!
from the women i had the pleasure to be intimate with, most of them preferred to be penetrated - at least the first time of the intercourse play - with a bare head. the skin of the glans is much smoother and the whole shape of the penis is more 'streamlined' enabling the penis to move forth and back as a whole and not inside the foreskin. take this comparison: take your erect member in your fist and move your dick back and forth while holding your fist in one position. now loosen your fist's grip and move your dick inside your fist. what is the difference in what you feel in your fist? now remember the sensitivity of the first vaginal centimeters and the sensation your glans' ridge causes.