In the K1000 server version 5.4.x, a new Machine Action variable was introduced, KACE_CUSTOM_INVENTORY_*.
The KACE_CUSTOM_INVENTORY_* field can be used to check a custom inventory value. The * will be replaced with the Display Name of the custom inventory rule. Only allowed characters are [A-Z0-9.-]. Anything else will be replaced with an '_' character.
For these instructions, I have used TeamViewer remote control as the example.
"C:\Program Files (x86)\teamviewer\version7\teamviewer.exe" -i KACE_CUSTOM_INVENTORY_TEAMVIEWERID
"%PROGRAMFILES%\teamviewer\version7\teamviewer.exe" -i KACE_CUSTOM_INVENTORY_TEAMVIEWERID
Once those are done, you can use your machine action to connect to a machine with their TeamViewer ID.
You can also click the little orange question mark next to the Machine Actions title on General settings. It more details on the custom inventory variable.