About a month ago I modified a cup holder to fit onto my Bugaboo frog. Although it's far from perfect, it's working out OK for me. I'm not sure what I started but it seems someone else has come up with a new solution. A Daddy Types reader has managed to make the Fold Up Stroller Drink Holder from Safety 1st work with the Bugaboo handle. There aren't any instructions for attaching it (maybe it just works with the Bugaboo like every other stroller), but there is a picture.
It looks a bit studier than my solution (which would definitely be an upgrade) but it doesn't look like you can take it off very easily; nor is the drink level. In the picture he also has one of the bag clips turned inward, so maybe he tried my way and wasn't satisfied. I'll have to get my hands on one of these cup holders and try it out for myself.
MacGyver A Bugaboo Cup Holder, Round 2 [Daddy Types]