Unless its <6 spots you should make room. In 12-team leagues I almost never carry a 2nd QB/TE/DEF/K. I would much rather hold 4 spots for handcuff/upside RBs and two spots for upside late pick WRs. It's working wonders so far, as I've had Knile Davis and Bernard Pierce on most teams, over WR4/5s or backup QBs. Those two are paying massive dividends this weekend. Just traded Pierce for a major WR upgrade (Jeffrey+Pierce for Julio).
Basically I think you need to go upside on your bench instead of bye-week fillers.
I'm thinking about doing this to be honest, just to try something different, especially with all the injuries and a losing record. Dropping all of the bye week fillers (F-Jax, Vereen, Wayne, etc), and load up on 4 of the top RB handcuffs. Trying to deal these guys in trades is nearly impossible for some reason. However, this will cause a few league members to spend some FAAB dollars on acquiring them while potentially dropping more under-the-radar prospects into the pool of free agents. Looking at the stat sheet, some of these backup guys are getting enough garbage time points that almost rivals what the fillers are already producing.
I'm not sure who else to list or how you would rank them in terms of preference, but it looks like these are the guys to have so far include:
CJ Anderson
Alfred Blue
Jerick McKinnon
Damien Willams
Robert Turbin
Storm Johnson
Silas Redd
Lance Dunbar
Latavius Murray