At this time, openocd does not have support for the dreamplug's SPI/NOR so it cannot be done. however you can use openocd to halt the dreamplug, transfer your uboot into memory, resume and flash with existing command.
Warning, do not flash just any u-boot code you got. your u-boot code need to be able to boot from SPI so use "mkimage -l -u-boot-filename" to check it is bootable from SPI.
Good luck
