Okay I went to uni in Leeds so there are a few ideas!
If you get to Leeds reasonably early on the Friday you could do the
Otley Run that link is much longer then we ever did - we would stop at the Oak as it had a huge beer garden to sit in till the pub shut, half way through the Otley Run you come to some cheap but tasty and fun restaurants:
Jino's Thai Cafe
Caliente Cafe - Tex Mex
Salvos - Italian
If you are getting to Leeds latish on Friday then I suggest staying in the center and heading to
the call lane area as there is loads of restaurants and bars around there.
I loved the birdcage but I'd say as a stag do it's probably not the right venue and it's alternative would be a lap dancing club (I don't know any im afraid!)
Could you organise TShirts for say the Friday night you can get them done reasonably cheaply a quick google brings up
this site. They aren't a huge cost and are a nice memento and can tie into a theme if you so wish!
Pranks and dares!
Come up with x number of dares e.g. down a pint, get a girls number, sing a song in public, get bought a drink, ask someone about there fave sex position all sorts of silly ones like that and you can either hand them out individually or come up with a tick list that the stags have to do!
At one of my friends hen party we asked every hen to come up with a dare! Wrote it up on to a piece of cardboard and strung it round her neck - as she did each one it got crossed off. The advantage to this is he should get some tame ones, extreme ones and original dares!!
What about asking each stag to bring a memory and a memento that is personal to your brother. The memento is a keep sake of his unmarried days and the memories are a nice way to break the ice. My friend did this slightly differently with everyone asked to bring a gift that reminded them of an 'Amy moment' she had to guess what the 'moment' was and who the gift came from these were as silly as a box of tea through to some highlighter pens, 90% of the moments were hilarious and had the table in stiches!
Don't organise to much people aren't interested in it once the booze starts to flow!
Other idea's:-
Get a photo frame and ask the stags to sign it - put in a photo of the stags and give it to your bro as a reminder of his day!
Make sure you have labels so people can put there name on display saves the awkwardness of sorry what's your name!
Book a table at a restaurant and ask if you can decorate the table - this can be done cheaply and quickly if you enlist the help of a couple of the stags.
Most of these ideas can be done in an email or two and maybe one shopping trip! Remember there is no harm asking the other stags for ideas as they will be delighted to help!