Using FF miles on complicated routes
 

I work for a charity and will be making a trip to Dhaka in December for a couple of weeks. Mrs G would like to join me, but paying for her fare is beyond our budget. Over the years, I've built up a large stack of FF miles flying around Africa with Air France and Kenyan Airways. My thoughts are that we could fly to Dhaka via Kuala Lumpur using either Malaysian or KLM using my miles to get Mrs G that far. There are a few options for getting from KL to Dhaka.

My question is, how do we go about getting tickets that cover sectors on two airlines, while using FF miles for one passenger on one sector? I'm sure others do this all the time, but I don't and I'm a bit thick!

Thanks