You can define mouse tools and call them from the rollout of an MCG tool.
To do this, simply define a mouse tool in the usual way and add a button to call it in the Custom UI property.
For example:
-- Define mouse tool before it is called tool myMouseCapture ( on mousePoint click do ( format "Captured click!!! % \n" click ) --Right-Click to stop ) rollout params "Parameters" ( -- Restore the default rollout <<ParamUIDefs>> <<RolloutParamsHandlers>> -- Define button to start mouse tool button ToolStart "Begin Mouse Capture" width:140 on ToolStart pressed do ( startTool myMouseCapture ) )