I have one each of Comice and Bartlett. I bought the Bartlett mainly to serve as pollinator for the Comice. Both were bought as bare root, not at the same time - I forget how much time passed between acquiring the two trees, but I think it was a week or two.

Both produce flowers, but not at the same time. The Comice blooms a good two weeks before the Bartlett. By the time the Bartlett blooms, the Comice flowers are done.

Are there any tricks I could use to force them to bloom together?