Not really 'hacking up' IMO. Go here and look at the 'pin seizure' pdf's for these, which are likely similar to the EBay units.
http://products.hirschmann.de//index.php?sessiontoken=20071013195317-11111111&manid=4&CFID=&CFTOKEN=&pbparam=tid=980,pid=776,spid=2,maid=26,view=2
I had one in the trunk of my SL when I got it, uninstalled. Took less than 1/2 hour with a multimeter to verify the pins in the harness plug.
All you need is ground (always a brown wire), 12V constant (ignition controlled), and a 12V signal from the radio, when it is turned on (and no 12V when it is turned off, the ''trigger wire').
Find the wires at the plug, and go various routes to connect to the antenna plug, supplied with the Hirschmann (and shown in the pdf schematics).