Sorry, but the usual delimiter for multi-entry ID3v2 tag fields is a semicolon and not a comma. You’re asking for Roon to deliberately break this convention.
The convention arose I suspect because of the requirement to support the “Last name, First name” sort ordering which some prefer to use, so that both choices could be supported, e.g.:
ARTIST: Fred Smith; Joe Bloggs
ARTIST: Smith, Fred; Bloggs, Joe