I put a little ace stem 45' rise about 50mm reach on my youngster's when 1st built or you could try a truvativ or similar DJ stem which would take a fair bit out of the reach too. Only problem is steering can get a bit twitchy!
PM me if any use as I've both spare (and a shim to fit std bars to the truvativ oversize stem)
Don't know if this is relevant to this thread but a guy called "oldshovel" on YouTube is building up some interesting builds. Here's the one for his daughter: