you can use the config reg command (it think ) to tell the router where to load from like a remote server, then you can have it load multiple configs from there by renaming configs to the config name loaded in the config reg...not sure if that is the command. (not at once...lol)
or you can tftp the multiple configs to the hard disk and copy config 1 run, or copy config 2 run, then write mem in case of power loss, no reboot necessary in that case, config change is instant.
Figured I'd check, pasted below from live 2621
memory Configure from NV memory
network Configure from a TFTP network host
overwrite-network Overwrite NV memory from TFTP network host
Configreg is for telling the router which memory register to load the config from, I think you can save different configs to differnet entry points and start from ROMMON mode to load indivisual ones. Maybe not.