the other option is try to sand/shave the stems little with sand paper or an exacto knife or something
Probably not a great idea, since it will be hard to get them all correctly sanded (or rather sanded in the same amount). After sanding all of the other caps will be loose.
Probably an awesome way would be for someone to create metal cherry stem top, which when heated up will fix the caps not the stems
Or tool presented in one of the links posted by rowdy might be a better idea (no heat treatment, just brute force plastic shaving).
I can see that more and more caps have issue of being too tight to fit. Is this a problem of certain cherry stems or is there a problem with keycaps moulding?