After puberty, when I had started ejaculating and become more embarrassed about my sex activities, all of my wanking was in private, alone. But I fantasized each time about earlier days, ie rubbing off with or against other boys. The solution was to use a full length mirror, which we had in the bathroom at home, as my partner.
I had always wanked in front of it before showering and often splattered it with cum. More and more I started 'fucking' it, rubbing my cock against the glass, sometime kissing myself. But it was hard to achieve a good orgasm against the smooth cold glass and I would nearly always have to finish myself off by hand. Eventually - I suppose at about 14 - I rigged up a rubbing pad, which was a piece of sponge rubber about 6 ins square and an inch thick, with a smooth silky piece of cloth wrapped around it. I placed this between my erect knob and the mirror and fucked the pad, so that (in the mirror image) I could see the underside of my cock emerge from and disappear behind a kind of wall, which looked some two inches thick. When it was out of view, it was being rubbed off against the material. I tried to time it so that my load shot out just as it emerged over the 'wall', hit the mirror and pool on top of the foam block.
To my sexed up teen brain, it was a horny substitute for rubbing off against another boy and cumming simultaneously.