you could always release the paid version the week before the free version and essentially get a double launch.
I think this is likely to be the way if first launch of game is paid. I can confirm that changing a game from paid to free makes no positive difference (without huge downloads I guess), not even with cross-promotion (advertising a paid game from within a free game).
Back in the day there were many games like this, with a paid and a 'lite' version. I think the model fits a small indie best, now that I've thought it through some more.