Silly question really, as I'm 99% sure you can, but wanted to check if anyone had done it before?

I am flying DL premium select west (upgraded from MC) & then on the same ticket VS upper class east (upgraded from Premium), but for at least the latter flight I want to use my SAS ff no. for it to count towards the SAS Millionaire promo (&, sadly, I believe even the meagre earnings thru SAS for a DL-marketed PS fare class flight will earn more than it would as a DL Diamond).

For the former, it'll make sense to leave the Skymiles no. in there for the chance of a complimentary upgrade to D1 & just pick up a short DL segment in between the two for SAS.

Anyone done this? Multiple Diamond line agents acted like I was on drugs when I asked if this was possible/the case.