We always agree on this site, that cucumbers are grown to die as soon as possible...
It really is a pain, and after several failures, I always succumb to a couple of plants from the GC eventually, so you may just have time to do the same, and bite the bullet! I've done this last week for the umpteenth year...
Best of luck - you can easily say that you tried, but then joined the majority crew in the end! There's a medal somewhere!
Actually, a chum next door is having the same problems, and I really do think that an early feed can help, especially if they seem to be in a sulk! I'll ask him how he got on!