Using ROWIDs as the primary keys for a table isn't really a good practice -- despite the fact that Oracle decided to include the capability in Apex. I will do it... on very rare occasions, when I have a tiny lookup table that really has no need of PKs. The best solution would be to switch to using a real primary key column for that table. That said, it may well not be a practical one for you.
You might try placing a process in the Page rendering section that runs before the row fetch. Have it do something like:
:P24_ROWID := REPLACE(:P24_ROWID, '%26#x2F;', '/');
Not something I've ever needed to attempt, so untested...