Pointools- Linear Clipping Boundary

Within Pointools cloud editing features, is it possible to somehow "reference", in an external boundary that could be used to clip, or extract the pointclouds within that predefined boundary/ polygon?

For example, if we have numerous point cloud tiles received from a contractor that cover a railway corridor, we ideally want to be able to create a pointcloud (s), along only a fairly small across-track swathe of the corridor (say, 10m), but obviously the linear distance could be quite large. 

From what I can see, manually drawing a polygon to select only those points would be difficult. Ideally, we would like to be able to create a point boundary in Microstation (offset track centreline for example to create polygon), and use within Pointools as a selection boundary prior to processing etc. 

Is there a way of doing something along these lines within Pointools? I appreciate it could be worked backwards- ie ref in the point clouds into Mstn, but we seem to struggle with point cloud manipulation within Mstn, whereas the point cloud engine within Pointools seems much quicker.