Hi PleasureFlights,
Your best bet is to contact an
RT examiner.
Looking through
CAP 804, section 6, it seems you would have to pass the PPL communications exam again & pass the RT practical test. There's no minimum training requirement so if you're up for it, you could do the whole thing in half a day. The syllabus is based on
CAP 413, there are
other training aids.
This would get you a stand-alone CAA radio licence, valid as long as your language proficency remains valid, so if level 6, valid for life. I have no idea how acceptable that is to the Danish or any other authorities when used with a Danish PPL.