I think you should try not to use the 2-4-1 so you just get 3 1 way Fs and then use the UC returns. Do you have enough miles for this?

Alternatively just get the Fs out and Ys return with the 2-4-1 and ALSO the UC tix and see if F class becomes availble. If so, just sell back the UC and if not, cancel the 2-4-1 and just use miles for the 1 way Fs.

I hope this makes sense!!