Thanks Tony - I had been using that exact same method for the past six weeks or so. I started to see some green (about as much as you see in the pics in my OP) but I was afraid that constantly disturbing the bags to check on them was slowing the growth, so I put it into a somewhat more permanent growing environment (death cubes).
I will have tried three different growing methods by the end of tonight. If I don't see anything in a few months, I'll just take the plunge and buy some live sphag and try to start growing that. Or, knowing me, I'll lose interest and do it sooner!