Hi Chris, you might want to try converting the STL file to .obj format and then use the OBJ to 3DM wireframe converter from here:
https://moi3d.com/wiki/Resources#Obj23dmWireframe_converter

That makes wireframe lines or closed polylines for each polygon instead of trying to construct a solid out of it which is much more heavyweight.

If you did want to edit this script to not try to join it into a solid, the joining part is done by a function named JoinTriangles(). The function is called on line number 17 in the file _STLimport.js . It's a long line of code, look for the piece of it that has this:

var solid=JoinTriangles(triangles);var sol=solid.numSolids;if(sol<1){var message="SORRY!\nI WAS NOT ABLE TO MAKE A SOLID!\nDont't try to \"Clean flat surfaces\"";}else{var message=sol+" SOLID CREATED!";};

Delete all of that or "comment it out" by putting /*    */ around it and then it shouldn't do the joining part.

- Michael