General Message Board
If you want somebody to replace McFadden, go Reece in my opinion. Jennings will get first crack at it in all probability but he's a garbage runner/receiver as we saw in Jax last year. Reece showed strong potential in both areas last year.
If Tate, Bell, Pierce, or maybe Brown are available they are also good adds in the order I posted for priority.
The players to handcuff to McFadden are Jennings and Reece. Jennings will most likely get the first crack at the job. Matthew provided a good list. Bell has the best chance to make an immediate impact even with Bush on the field. The only player I'd add to that list is Christine Michael (Seahawks).
Handcuffs are only good to you if you pair them up with the starter that you drafted. Otherwise, you are just taking a part-time player who will only be useful to you if their starter gets injured.
Ben Tate, Bryce Brown, Bernard Pierce and Joigue Bell are good handcuffs.
Marcel Reece took over for DMC last year when he got injured, and Rashad Jennings was the only other Oakland RB to get a touch week 1.
Ronnie Brown and Danny Woodhead are the best options if you would prefer to wait for Ryan Matthews to get injured.
Roy Helu and Isaiah Pead are some other options.