My colleague is part-owner of The Vintage at Drygate in Duke Street, Glasgow - a great venue with a beer hall serving a wide range of craft beers and good food.
If anyone organising coaches (or indeed cars or pedestrians!) is still looking for a lunch stop then this venue can accommodate hundreds, has plenty on-site coach parking and is a short drive from Hampden. They're open anyway but will designate themselves an ICT venue and gear up accordingly if there is enough interest and they get some advance notice.
Let me know if you're looking for somewhere with good food and drink. Details at http://drygate.com/the-vintage/