Hi Hunt,
You will have to use BAT:
1/ With BAT, configure the current "Phone Load" on every phone. Then they won't upgrade their Firmware after the upgrade to 7.
2/ Site after site, also with BAT, clear the phone load parameter on every phones of the site. Only these phones will upgrade.
You can also try to enable the "Peer Firmware Sharing" on the phone configuration page, after the upgrade to CUCM 7. I've never used it, but it's been created for WAN Bandwidth limitations problem during Firmware Upgrade.
jp