Thanks for all your help guys, I've finally managed to get my hands on some hatchling crickets, which he's now demolishing at an astonishing rate! I'm still using the feeding tank so I can monitor his intake and get him up to a healthy weight. He's eating roughly 15-20 pinheads in a sitting, possibly more because I leave him in the tank with some and obviously it's hard to see what he's getting up to in there! Hopefully he'll be ok now until the fruit flies arrive!
Thanks again!