Alternate Sneak Attack rules when there are no HP rules

Sneak Attack - roll an extra amount of your weapon damage dice equal to the number of d6s you would have rolled for sneak attack. Keep only one attack dice from those rolled. Every time you rolled max value, past the first, you divide the DR by 1 plus the no. of times you rolled max value on a die.
Use the 1d notification to show how many additional dice you would have rolled.

Ex. With a long sword and +2d sneak attack, a rogue rolls 3d8. He rolls 8, 8, & 3. He takes the 8 and deals max damage but since he rolled another 8, he divides the DR by 2.
With daggers and low value die there is a higher chance to make an armor piercing strike vs larger weapons which bigger die values.

A very skilled rogue uses a shorts word or rapier and has +3d, he has the feat deadly precision. He makes a successful sneak attack - he rolls 4d6: 3, 1, 6, and 1. He retools the two 1s: 3, 4, 6, & 6. So the rogue deals 6 damage and halts the DR.

It's funny that smaller characters with their smaller die like d2, d3, d4 and d6 have much higher chance to make an armor piercing strike. If the character has rapid shot, and two weapon attack there are numbers to play.