in order to lower the gears on my dad's bike (11sp campag) took the 11-23 cassette off along with the freehub. replaced the freehub with the shimano one, took the 11sp 11-28 cassette off the smart trainer and installed it on the rear wheel. couldn't find the 11t lockring anywhere, so used spare cassette's (10sp ultegra 12-23) top sprocket along with the 12t lockring. the cassette starts 12,12,13,14.. which is a bit of a bodge but i bet he'll not miss the 53×11 top gear.
installed the campag 11sp 11-23 on the trainer for which it's perfect.