I used to play a violin years ago and had metal adjusters at the end of each string where it entered the tailpiece. These were for fine-tuning but there was quite a bit of leeway and they could be used instead of the tuning pegs if the strings were only slightly out. Would that help in any way? Alternatively, a bit of bow resin around the peg makes it stick in the hole for a while, but depends how worn the hole is.