I know this was posted awhile ago, but if you or anyone else is interested, the original samsung galaxy tab HDMI dock uses the same connector and works w/ the 7.7 (I know because i have a couple). You can get these on amazon for $15 right now. I believe this is the same dock for all the tabs and they just change the plastic piece that holds your tablet to accomodate the model (i have the original galaxy tab, the 7 Plus, and the 7.7 and they ALL work).
If you take it apart, the tablet connector looks exactly like what you are looking for - an L shaped 30-pin. The profile when plugged in is very thin and looks less like when you have the actual car charger cable plugged directly into the tablet.
I've attached a picture of what the cable end looks like. The nice thing is if you keep all the electronics intact, there is an area in the back that the car charger cable connects to pass power to this cable as well as a 3.5 jack for your auxiliary audio connector. Once you lop off the plastic tablet holder part, you have a bare ribbon cable that you can cover in black electrical tape and you just have to mount the pod onto the back of a hard tablet mount and plug your power and auxiliary audio cable into it.