as long as you are using vc paper, and you can put the light through your filter
you shouldn't have any trouble split filtering your paper negatives.
in a film photography forecast interview with a fellow appuger david william white
i learned a trick that i had never thought of before ... i removed my lens from the enlarger
and just project the light straight down. i have a vc filter holder i can slide over and it works perfectly !
good luck !