I’ve read that interstems for quince, hawthorne, and mountain ash that the pears Beure Hardy, Old Home, Anjou, and Comice are the most successful types used as interstems. It might pay to have some interstem scion trees on hand. I’ve had great success with clapps favorite and clara frijs grafting on stubborn wild callery trees. I will graft more this year though should also mention my douglas pears had a 100% take rate on all callery I tried them on which was 5. Some pears are easier to graft than others. One study that documents hawthorne, and mountain ash interstem pear varieties can be viewed here http://horticulture.oregonstate.edu/system/files/ond100203a.pdf. Beure Hardy is used as an interstem for quince as noted here in a study done by the usda http://portal.nifa.usda.gov/web/crisprojectpages/0423049-cold-hardy-and-fire-blight-resistant-quince-propagation-rapid-multiplication-and-field-trials.html. To further backup the Beure hardy as an interstem for quince note it being used here Maple Grove Nursery - Rootstock. This is another interesting article on rootstocks and interstems if you have the time http://www.orangepippintrees.co.uk/articles/rootstocks-for-pears