SIP.CONF and use of templates for repetitve configurations

Regarding the use of templates in sip.conf:

voip-info.org/wiki/view/Aste … g+template

Is there a way to have the following option to be set something to this effect:
mailbox=username@context

I have 1000 users (aka extensions) and I’m using templates for common settings. These 1000 users dialing AND voicemail context changes very often. It would be a pain in the butt to change 1000 users voicemail context each time. Anyone know how I can make it so its a common setting.

example of how I have it now:

[commonSetting]
context=outbound
type=friend
nat=no
canreinvite=yes

[1000](commonSetting]
mailbox=1000@customer1

[1001](commonSetting]
mailbox=1001@customer1

Its a pain to update 1000 users to change the voicemail context.

Looking for a way to do something to this effect:

[commonSetting]
mailbox=$user@customerX

That way I change one line and affects all users