For Christmass I helped my mother do a two and a half bird stuff.
1. Large chicken
2. Pheasant
3. Sausage meet, onion and apricot stuffing.
You could replace the sausage meet with the haggis. Maybe swap the apricots for something else I’m not too sure what, part of me says dates, part of me says keep the apricots.
Bone both birds, place pheasant inside chicken, stuff sausage meat (or haggis in your case) in gaps, sew the chicken back together again, cover in streaky bacon and roast. The end result was not at all dry. I think the apricots helped. Tasted lovely, but a lot of meat!