Well, that's a problem which makes the idea totally useless for multiplayer. It would be annoying to rejoin again and again. In SP you could just cheat, in case tell the player that he should cheat if he gets stuck.
To lower the stuckness (is that a word? ) one could mark the areas where blocks appear.

Also, what about a timer using the shield. At the start you get a shield and right after that you activate the system. It could be made in a way, that the timer from the shield is the same than the one for the walls.