Hi Todd,
Shorting pins 1 and 2 on the REG bus using either a relay or opto-isolator should do what you need as long as the dip switches on the charger are set properly. The BMS has an output that can directly control the opto-isolator or a small relay (< 100mA coil @12v). I started working on a schematic along with a drawing of the position of the dip switches for you, but I have to leave the office in a few minutes for the weekend, so I will have to complete that on Monday.
For best redundancy and reliability (always a good idea when working with an expensive battery pack), a contactor / relay should also be added to the AC power to the Manzanita Micro charger in the event that something malfunctions with the REG bus or with the charger itself (i.e. a dip switch is accidentally changed, charger malfunctions, etc.) The OrionBMS has 2 contactor outputs for controlling the charger, one for normal use, and the second for backup method. If the BMS has to resort to the backup contactor, it will set and store an error code as a safety. Looking online there are some people who have reported the charger has continued to charge after the REG bus was commanding it to stop, so I would strongly recommend the backup.
If you let me know what motor controller you use, I can also see possible options for integrating the BMS with that for you too.
Thanks,
Chris