As far as the strategy goes... it depends on how much room you have to pick up an extra MRP with a good WHIP. If you have enough room to pick 1,2,or 3 of them without hurting yourself else where, it might help pick up a point or two. Also you might look at benching Lackey depending on matchup or picking up a lower-WHIP SP or two.
Here's how the MRPs will affect you:
You said you were behind in IP, so I'll say assuming 883 IP with a 1.25 WHIP so that you're currently on pace for 1180 IP of 1.25 WHIP total, and that MRPs will get at least 20 IP remaining for you.
By picking up a Rafael Betancourt (0.74 WHIP), your WHIP will bump down to 1.242.
Picking up a couple Rafael Betancourt, R Soriano (0.95 WHIP) types, get you WHIP to 1.237.
Picking up three guys - Rafael Betancourt, R Soriano and Heath Bell (1.02) , you could end up with 1220 IP of 1.233, which might be good enough to challenge for first.
MRPs aren't going to drastically change anything, but if you have the room on your roster it could help get a couple extra points.