yup I'd go with some light lat pulldowns or bent over rows follow something like the warmup the Max-OT program advocates ad I rekon you can't go too far wrong (not sold on the whole workout just yet but the warmups are the bomb

)
here's a basic idea (
lat pulldown ... assume your max is 100lbs - for ease of figures

)
12 reps @ 20lbs
10 reps @ 30lbs
6 reps @ 40lbs
3 reps @ 50lbs
1 rep @ 60 or 70 lbs
then have at it using your
max weight (for me, having used the good old 'set of 15 at c.65%max weight' as a warmup I have noticed my working max weights rise noticeably). As a warmup for chins I don't see why it should be different, just do some chins afterwards instead of max weight pulldowns
hope this was helpful.