Several years ago I played in a group that used what they called The Inverse Rule for rolling cure spells. I liked it enough to add it to the game I now run. On a d8 1=8, 2=7, 3=4, 4=4, 5=5, 6=6, 7=7, 8=8 so the minimum possible cure is half.
Just remember, what's good for the party is good for the enemy. ;-)
Why not just roll 1d4+4 in place of the d8?