How if you just set the "multiply" factor to 0 ?
I don't want to try it out on my community but as far as I understand the system, a multiplication by 0 should result in all score set by 0 !
Afterward, or you let the multiply factor by 0 (so the points never get back), or you set it to 1 (scores will be up and down by the votes as normal) or you set it by the value of your choice (default seems to be 10).