Hey there mate, I'm just learning the fundamentals of trials and my friend Chris (El Cristoff) was helping me to learn sidehops just the other day. He told me that when I'm on the back wheel right next to the wall and i've got the balance point just right, to preload. And he showed me that preloading for a sidehop is basically the same principal as preloading to do a gap, so practically just lowering down the front wheel till it's right near the ground, Then use all your strength to rocket yourself up, (both wheels at the same time). Give it a go and say how it goes