Help with Shrinkwraped sculpted geometry on retopo'ed character

So i’ve been having issues with my character workflow lately and i’m not sure if i’ve been doing it right and could use some help, specifically my problem is with the shrinkwrap modifier and the mouth. After i have sculpted a character i retopo it and add a mouthbag on the inside but when i add a shrinkwrap modifier to the lowpoly mesh the mouthbag obviously contours to the outside mesh because the sculpt doesn’t have a mouth cavity. So my question is; do i need to sculpt my character with a mouth cavity or do i have to have the moddeled mouth a seperate object? I have tried using the vertex group of the shrinkwrap modifier and it helped but it leaves some artifacts and glitches on the extremities.
Thank you for you help!

I would shrink wrap without mouth bag with sealed lips and model it later.

Exclude your mouthbag vertices from the shrinkwrap modifier with a weighted vertex group.