I live in LA and have started going to LA Galaxy games fairly frequently but I haven't seen much of Jack because he is far down the pecking order. Jack is LA's 4th or 5th choice striker behind Robbie Keane, Mike Magee, Dos Santos and possibly others.
I would imagine that LA have agreed to pay most or all of his wages during his 6 month trial period. LA is a rich club as it has wealthy supporters and average attendances of 25,000+.
This season Jack has been playing in the USL which is about National League North and South standard. I doubt TM will put him straight into the first team.