Outbound Trunk Groups

We have 4 analog lines. For DAHDI Trunks, I have the options of:

Group 0 Round Robin Ascending, etc., (This Group 0 includes lines 1 - 4)
Analog Channel 1
Analog Channel 2
Analog Channel 3
Analog Channel 4

I want to only call out through Channels 1 - 3, because the phone company caller ID is overriding what I’m setting in FreePBX as the caller ID, and Channel 4 actually belongs to a sister company in the building.

Is there a way to make a custom group that includes lines 1 - 3, but not 4? Or just to block line 4?

I’ve tried a lot of things, but zero have worked. A way to edit what is in Group 0 seems like it would do exactly what I want.

Thanks for any help…