Hi Ian
I have not made pure bunny burgers but have made game burgers with bunny in. I used some of Franco's game mix for the burgers and although it was a little salty, it was OK.
I tend to use a lot of thyme in my game sausage, pie of burger preperation but like a lot of people I tend to go on eye rather than measure things out, which is no good if you want to pass a recipe on
but in essence I use Thyme, garlic, mustard seed and a dried fruit such as cranberries. I use some breadcrumb and bind with egg. As HF has just said you will need a good proportion of fat as bunnies as well as all other game is really void of fat so needs to be replaced - or of course have a very dry product!
Cheers WW