First off - I believe Ample Hill is at Boardwalk. I'm thinking they may want Beaches and Cream.
Depends on where you want to be after having ice cream. I like Katieeldr's suggestion, especially if you want to go to Epcot afterwards. If you want to end up at HS, I'm thinking it may be easier to go to TTC from the Poly and catch a bus from there to BC - but I'm not sure if that exists. If it does then after the ice cream take the Skyliner from IG to CBR and tranfer to the one going to HS. If you are not going to a park after, then after the ice cream I'd take the boat from BW to HS then a bus at HS back to the Poly.
I should note that I believe the boat ride from BW to HS would take less than half the time it would take doing the Skyliner routes to get to HS.