Amazon.com: EKLIPES Motorcycle, ATV, Jet Ski Snowmobile Cell Phone and GPS Adapter: Automotive
this may help ya. similar to slows idea.
Scrappy found the Eklipes "Generic" Accessory 12V receptacle with the opposite end able to cable up to your Battery Tender end (I found it after I used the HD one wiring it up to the Battery Tender plug, but double check your receptacle wiring as the shell should be ground, the center button +12V DC and fused between 2.5 and 7.5A typically.

Otherwise use the similar one for HD Touring bike that has the Deutsch 4 pin connector on the opposite end to wire directly into the HD wiring harness. Either option works. Good Luck. :s