If you can handle the pain... that leuytolyce(sp?)/Pgf2a... I don't know if I got that right... but supposedly it is supposed to help lagging body parts... there are some posts on it... do a search.
Winstrol and test suspension supposedly work for localized injections. But I think if a specific bodypart is lagging, you should tweak your routine a little to make sure you're putting enough stress on that bodypart.
try mesing with your training first. my rear delts were lagging bad, all i did was start doing 3 sets of rear delt laterals with low weight, every second day. my shoulders are killer now.