heres the best way i have found that works well.also charges eithier one with 5.5 volts as required.connects to battery and has rca jacks that you can connect to a patch cord that is rca to 1/8 for aux plug on radio.heres the link for the iphone adapter and the patch cord is about $4 on ebay.i also used this on my gl1500 and worked great.one cord for charging and play back,all goes inside fairing.iphone end is long enough to reach outside to mount iphone on bars.
instead of going to the rca to 1/8 plug, i would just add the rca jacks to the radio. i saw a schematic that showed which pins were the rca in r/l and ground. (or you could send your radio to iron cross).
this is a pretty cool intermediate solution, but i really like the ipod controller that works with your radio and the hand controls. but it is much cheaper, and cheap is good