I do exactly as the OP suggested ... I use the second half of the copy to politely request that they keep my FFL on file and that I hope to do business with them in the near future. I have never been asked for any more identification than my FFL, so I don't send anything else like a DL.
Don't forget to send it in to MidwayUSA and Brownells ... you qualify for healthy discounts from both of them.
ps ... the bore-select 91/30's at J&G Sales are in really good shape (wood too, not just the bore) ... that might be a good first acquisition to try your C&R out on