If the rest of the board is brand new, you can probably do the "lite" version of the bolt mod: drill out and bolt up only the broken rivets. This is much less work because you don't disassemble and reassemble the main assembly. Once you have the tools (dremel, drill bit, nuts, bolts, 5.5mm driver) the ersatz bolt mod takes only a few minutes.
You wouldn't be able to change out the membranes or springs, but on a NIB SSK those should be perfect already.
For those that haven't seen an M taken apart: there's nothing but solid plastic between the stud that the rivet was formerly attached to, and the front of the barrel plate. From the metal plate side, you can drill straight down into the stud and through to the barrel plate without disturbing anything important.
You'd want to remove a few keys opposite each spot you drill, so they aren't damaged. (But don't take all the keys off, because then you're sitting the board on its springs which could damage the springs.)