Bash completion own compgen prefix

I have a simple bash completion script that essentially invokes my (non-bash) program and set its output to COMREPLY, i.e.

COMPREPLY=( $(my-program -- "${COMP_WORDS[@]}") )

Some of the options accept comma separated value, is there a way to handle suggestion only for the last item? Let's say the user types -v opt1,opt2,o, let's say my program finds out the the valid options at this point are opt3 or opt4. If I just return those 2 and press TAB the output changes to just o (entire prefix gone). It works if I return opt1,opt2,opt3 and opt1,opt2,opt4, but that doesn't look nice. Possible solution is to do something like https://unix.stackexchange.com/questions/124539/bash-completion-for-comma-separated-values , that is, invoke my-program to generate [opt3, opt4], and pass that as word list to compgen with opt1,opt2, as prefix. But that requires duplicating some logic in the bash script as in my-program . Is there a better way?