Kick the spare tire pressure up to about 40-psi and you won't have to worry about it a for a long time.
But check the max pressure indicated on tire. My Michelins (on 09RX350AWD) indicate a max pressure of 35psi, and that is exactly what I put on (in?) the spare. In any case, even apart from the TMPS, it is a lot easier to deflate a spare tire a little when you need it than to inflate it - and you don't need to check it as often.