My suggestion: don't use an expensive cartridge for the first play after the cleaning!
It will be difficult for anyone to advise sensibly without knowing what specific glue was used. Even if someone had a similar problem and reached a successful outcome, one couldn't assume their cleaning method would work on an LP from a different plant, or even the same plant but from a different time.
Some glues are removable by chemicals that won't damage vinyl. Some aren't. On the assumption that LP manufacturers choose glues that bond effectively and permanently to vinyl, I'm not optimistic. OTOH, the side isn't playable now. If he wrecks it trying to save it he won't really have lost anything.
It will be difficult for anyone to advise sensibly without knowing what specific glue was used. Even if someone had a similar problem and reached a successful outcome, one couldn't assume their cleaning method would work on an LP from a different plant, or even the same plant but from a different time.
Some glues are removable by chemicals that won't damage vinyl. Some aren't. On the assumption that LP manufacturers choose glues that bond effectively and permanently to vinyl, I'm not optimistic. OTOH, the side isn't playable now. If he wrecks it trying to save it he won't really have lost anything.