This sequence may be better than what I originally posted:
i2c dev 0;i2c mw 0x58 0x00 0x00;i2c mw 0x58 0x96 0xdf;i2c mw 0x58 0x4a 0x20;i2c mw 0x58 0x4b 0x80;i2c mw 0x58 0x06 0x4;i2c mw 0x58 0x0e 0x68;
It configures the power sequencer standby mode (PART_DOWN pointer) to be the same as the last step of the SYSTEM power domain sequence, and then enters standby mode. The same 1-second tick alarm trick as before is used to wake the system back up again.
The way the PMIC power sequencer is programmed, this should leave all power supplies enabled (provided I understood the datasheet correctly, and read and decoded the register settings correctly).
The previous command moved the power sequencer all the way back to slot 0, turning off all but the default supplies.