Multiple partitions and boot manager on USB stick

Apologies if this is a stupid question, but can I use gpart to create multiple partitions on a USB stick and then install a boot manager to boot from any particular partition?
A wise man learns more from asking a stupid question than a stupid man learns from a wise answer ;)

Anyway, yes, that should be possible. Note however that boot0cfg(8) only works for UFS and MBR partitioned disks.