SMCLK on Calibrated DCO, Watchdog Timer on VLO/ACLK?

I always use the calibrated 1 MHz DCO as the main code clock. This sets the SMCLK to the DCO.

BSCTL1 = CALBC1_1MHZ;
DCOCTL = CALDCO_1MHZ;

I currently use the Watchdog in timer mode, set to SMCLK divided by 32. This gives me 32 interrupts per second (1 Mhz / 32 = 31.25 kHz).

WDTCTL = WDT_MDLY_32;

Problem is that this when I am using the Watchdog on the SMCLK, I can't go lower than LPM0 (SMCLK + DCO), which is a power hog compared to LPM3 (ACLK on).

I also don't want to use the external crystal.

So, how can I use the Watchdog timer on the VLO/ACLK, while keeping the main on the calibrated MCLK/SMCLK/DCO?