Hi Lucy, I see no-one has answered you yet. A friend of mine is on Byetta and he sure drinks. The only concern I am aware of is that the alcohol may decrease your Blood sugar and increase your risk of a hypo.
Have a look here: http://diabetes.emedtv.com/byetta/byetta-and-alcohol.html
Patient information leaflet for Byetta her - no mention of alcohol, so I guess there is no problem - http://www.medicines.org.uk/emc/medicine/19245/PIL/