I've done a lot of this in China, rarely with a prepared curriculum (and wishing I didn't the few times I did...).

A couple of questions occur...

1) How much English do the students actually speak? This will set the line between how much 'English' and how much 'Business' you'll be teaching...

2) What do the students do? 'Business' covers a lot of ground...finding out what your guys do might help you narrow your emphasis.

One good general approach I used was to focus on Business Communications...various kinds of e-mails, reports, phone calls, letters, presentations, and so on.
This is something almost all Business workers have to do, and also provides a good format for focusing on language and correcting demonstrated problems. There are books on this in China (I wrote one myself) but it's not too hard to design projects in BizCom...