I'm pretty sure that whoever is going to do the reverse engineering on this software will have to have this radio card u speak of, to see if the hack will actually work or not. I don`t have this card, and I am not sure if I currently have the abilty to do this, so your best bet is to probably DIY... Anyway here's some tips to get u started if u choose that route:
1) Download and learn to use an assembley debugger called Numega Softice (it`s all over the net), it`s amazingly powerful, but a bit of a ***** to use at first. If the software you are talking of stores the rds data in a specific memory address/location, you could find it with softice, and program your software to access this memory location.
2) Look at a few reverse engineering articles (again, all over the net), and you should be able find all the info u need to do this. Fravia's page of reverse engineering was exellent, but it`s not there anymore... Theres still a few mirrors around tho, and has articles for almost all abilities.
If u attempt this, good luck!