If you pull the IP connections from the gateway your IP Phones won't work.
The best suggestion I've seen is to modify the MGC list, although I didn't read the post clearly enough before throwing my ring into that circle.
1) Show mgc list - Write down the IP's listed
2) Clear MGC List
3) Set MGC LIST xxx.xxx.xxx.xxx (LSP Address ONLY)
4) Reset MGP
5) Your gateway is now in LSP mode, however any IP Phones will still register to your main site, since at that moment they can still talk to the main site.
Once you're finished with your WAN maintenance to set everything back:
1) Clear MGC List
2) Set mgc list xxx.xxx.xxx.xxx (and all other IP's from step 1 in the original order)
3) Reset mgp
I just did this for a client this weekend....
Good luck!