Hi hope this might help. I have an Onda v972 and use CM10.2 custom rom. This gives me BT capability but I still need to use a BT dongle. I bought this one.
PC trading mini USB BT dongle adaptor- supports win XP,Vista,7,8 and Android from Amazon, dirt cheap.
They all work with V972 and Zenithink c91. Just one problem, using BT dongle does eat battery life. I'm lucky if I get 4 hrs using it. but it works with 2xBT keyboards +other BT attachments.
Hope that helps.