This might be one of those situations where, despite sounding interesting and cool, the idea isn't actually a good one.
I'd say scrap the plan entirely.
But if you're definitely gonna try it, why not just let people buy in for a full stack whenever they get there?
Yeah I just want to try it, just for fun. See how it goes. I think thats the way to do it. Let them buy their $20 stack (10/10/12/1) when they arrive. But are there any downsides to having them not post blinds if they are late (i.e. is it unfair to any of the other players?).