I thought the 110% was automatic with the PM in the system anymore? So you don't have to argue with them, etc. Maybe they're just starting to roll it out, then ymmv or something. Anyhow, this deal should be pretty easy to work, practically the same exact setup with the z340s back in October. This is what you do:
1) Go to Staples, grab circular.
2) Go to BB, buy MX300 at the cash register, get receipt, rebate form, rebate receipt.
3) Leave BB, dump MX300, rebate form, rebate receipt in the car.
4) Go back in to BB with the main receipt and Staples circular only, nothing else.
5) Ask for PM.
If they refuse PM because there is a rebate, tell them that you can go over to Staples right now and pick up the MX300 for less than BB gives it to you even after the rebate, and that if they don't give you the PM you'll return the MX300 immediately and go pick it up at Staples. (And, if you want to argue the policy some too, you can add something in about calling the BBB about violating a posted store {and chain} policy.) To help matters along, you can even mention things along the lines of "I never send those damn rebates in anyhow because I did one or two a couple years back and they never came in the mail - it's just a scam to get you to buy the stuff" and try to ease the pain.
With the z340s, I was inexperienced (only my second hot deal) and the CSR practically rejected my PM before I even opened up the ad. BB tried to screw around by lowering their price from $xx.99 to $xx.94 so that the listed price minus the MIR was actually lower than the listed price at the PMing store (OM I think). But after I got home I calculated the numbers and figured out that after tax BB's was more expensive - besides the fact that you would have to use a stamp and wait several weeks for the MIR to come in. I came back and the PM came through.
-