Not sure but you might be able to listen to just the B1 Dispatchers but you would miss every other transmission. That would be by entering the RID info in like I-CALL/Private call.
So you would program like a talkgroup but use the decimal before the number and use the radio ID of the console. For example, if the dispatcher consoles used RIDs 65001, 65002, and 65003, you might enter them in as:
B1 Console 1 i65001
B1 Console 2 i65002
B1 Console 3 i65003
I don't know that it will work but it should. These are not B1's IDs, you will have to monitor the TRS with a scanner that can display them to determine what to enter. You will need to put them in a separate Group than the Troop TGIDs so you can scan only the IDs. Can't hurt to try it.
chris
The assumption of the foregoing suggestion is that if the Trooper's radio sends a talkgroup channel grant request ISW, which results in a talkgroup channel grant OSW, a scanner users receiver programmed to follow a private call channel grant OSW would follow to the assigned voice channel. I would be surprised if that assumption is correct.
On the other hand, I seem to recall that the PSR-500/-600 receivers can be programmed via Don Starr's WIN500 software to emit a beep if it detects a specified UserID. If my recollection is correct, the OP could use this feature, not to mute non-B1 traffic, but to be alerted to traffic in which a B1 "dispatcher" is involved.
The problem with this whole approach is that, as Bill and Gordon observe, Troopers assigned to desk duty do not access the system via a console port, but rather as a subscriber, which means that as often as not, the desk Trooper is using his personal radio, which will show his personal RID versus the RID assigned to the station's control station.