Lay cleaned blueberries on a waxed paper lined dish and freeze for at least 30 minutes.
When blueberries are frozen, make the chocolate ganache:
Place the unsweetened chocolate in a heatproof bowl to melt over a pan of simmering water. Whisk in sugar substitute, and as needed, thin with water and cream and blend thoroughly (use more or less than 1 tablespoon, as needed). Turn heat off, leaving bowl over hot water.
Dip frozen blueberries a few at a time into the warm chocolate, remove quickly with a fork, and put them back on the waxed papered dish. Spread them around so that they don't make big bunches, and then put them back into the freezer for just a couple more minutes. Alternatively, put the blueberries on a freezer-safe plate, pour the ganache over top, and then separate with a fork. Put plate in the freezer for a few more minutes. Serve frozen and eat quickly before they melt.