Rather than moving filament to a spool with bigger diameter, just use a smaller spool holder. This holder will be able to hold as small as 1.25" and does contain a retention feature. It's made to be a quick exchange for the standard Makerbot spool holder versions 2 and 2X. The 2nd file is an anchor that you can keep the spool holder mounted to your machine so it doesn't get lost. To use it you'll need to exchange one of the back door mounting screws with a longer one (6MM x 12MM socket head). The anchor has a detent to keep the spool holder from detaching easily.

MakerBot

MakerBot Replicator 2X

No

No

low

9%

infill can be whatever you want.

Used Autodesk Inventor for each part. The anchor has a small detent so that the spool holder stays put.