That can work fine and serves the same purpose on the trainer as if it was setup on a bike.
What is the actual bike planned for this combo?
Depending on the bike he has, getting proper chain tension could be an issue. It’s possible to setup a derailleur for good alignment, or even use a single speed tensioner to convert a regular geared bike if that’s the plan.
Do note that a typical single speed bike is not a good fit for this, due to the typical 120mm axle width that is not support by any DD trainers I have seen. Not to mention getting chain tension with slotted dropouts is also tricky with these trainers.
For now he will be using my busted (and too big for me) 2012 b16.
Since he is not shifting (you can shift the front because of a busted cable guide) it should serve him well for now.
There’s a bunch of cheap no-name cassettes for about the same price, and REI seems to be selling a Microshift for $25. I’d get a real cassette. (but maybe I’m not one to talk because I’ve been using 8 and 9 speed cassettes I happen to have, and also not shifting)
Not all single speed bikes use the track standard 120mm but it is something you need to check - easiest to try and drop a “normal” wheel into the rear dropouts. If it is an actual track bike it’s unlikely to have mounting points for either a derailleur or a tensioner but you could fit a chainring tensioner.
Putting my money where my mouth is I just ordered a Microshift 11-28 to replace my 8-speed. I figure I’ll put it on the trainer then maybe try it outside when the weather improves (I have 11-25 now).
I guess the Felt has internal routing and might be uneconomical to repair, but maybe for trainer use you could bodge something up externally.
The felt has a rivets attached guide on the last section before the front derailleur. That things goes behind the cranks and it’s hard to see if you are not looking, so i had no idea so i never cleaned it. Turns out that little thing is needed to keep tension. And since I didn’t clean it eventually broke …
There is no way to fix that i am aware. But like you said… This is for trainer only.
Largely off topic, but if you were interested in making a functional front derailleur setup, the latest generation of Shimano front derailleurs can be used with a full run of cable housing. That would be full length from the shifter to the derailleur body and might sidestep the failed mount.
(See page 17 showing the full run connection to the derailleur.)