When you gap to front, cock your stem - push your whole body weight into the stem to keep it on the back wheel. Obviously, don't do it to the point you go over the bars. Then, you should be enough balanced on the front wheel to either swing the back wheel round onto the object, or to wheelswap - let the front brake off whilst quickly switching your weight to the back wheel, pushing the bike forwards and up a bit so you get to back wheel. You can practise those on the flat, but you really need to learn to do the key thing for any of these moves - cocking the stem As for the brake, I use mine locked, partislly because I don't have much choice with it. You can land with it less on if you're able to wheelswap well already, I think. I'm not good at gaps to front, mind, I can only do them on flat, but when I do them right my whole weight is over the front of my bike.