Personally I don't fly the B model much, but if I get in that situation with a D model, generally I wait till he gets about D700 off my 6, then I'll pull back on the stick, drop one notch of flaps and loop, but I won't push it till I black out, cus it will burn too much E. When I pass the top of the loop I raise flaps and wep to get my speed back up. Sometimes I'll do this with a yo-yo as well. The one thing you really don't want to do with a pony is flat turn it. I don't know a whole lot about ACM, but flat turning a pony takes away your best friend which is speed. So generally I keep him looping, and maybe even throw in a yo - yo till he makes a mistake (many la la pilots are new to the game and can't control it as well, however there are others, i.e. shane who aren't going to fall for this well). If I get real desperate I'll pull a loop dropping flaps as I go around the loop, raising them at the end, your loops get tighter, but your speed also drops.
La-Las are tough, especially low, if you don't think you can get one up above 10k, try and play with him long enough for him to make a mistake. This is of course a 1vs1 scenario, if his friends come around, good luck to ya =P