You can actually build "empty" Behaviours and select the globally available actions (which includes actions from the Virtual Mouse) from other Behaviours at Behaviour Construction Kit > Behaviour Factory > [Your Behaviour] > Default mapping.

You can create such an "empty" Behaviour by pressing the plus button at BCK > Behaviour Factory, then unselect the top three checkboxes in the "Specification and Metadata" tab, so that the Behaviour isn't bound to a particular application. Then, enter a name, change the identifier to "com.peter.virtualmouseclone".

Because the cloned virtual mouse wouldn't be associated with any particular application, we'd need to make sure that Remote Buddy doesn't automatically switch to another Behaviour until before you explicitly tell it to stop controlling the cloned virtual mouse. Therefore, go to the Action Factory and create an action with this AppleScript snippet:

behaviourcore accessor "setActiveBehaviour" identifier "com.peter.virtualmouseclone" useActivationEventCode "activatedInFront" with stickyValue

(all in one line)

Then, jump back to the Behaviour Factory, go to the "Actions" tab and drag and drop the newly created action from the left list to the right.

Now, switch to the "Default mapping" tab. There, select the newly created action for "Events > On manual activation". Then select the actions you want to assign for the respective buttons.

Finally, use the gears button and select "Compile, test and permanently install scripted Behaviour".

Best regards, 
Felix Schwarz