Hiding elements from completion menu

I have implemented editing empty lines as shown in the editor cookbook: https://confluence.jetbrains.com/display/MPSD34/Editor+cookbook#Editorcookbook-Makeemptylineshelpfultofurtherediting

Currently, whenever I want to replace an empty line, more concepts than I'd like to have show up as possible candidates in the code completion popup:

Is it possible to hide "/*", "//" and "EmptyLine" from the completion menu while still allowing these concepts to be inserted at this position, thus only leaving "npc" in the completion list?

All of these items extend a shared base concept and I'm already sorting out some component types completely using a can-be-parent constraint. However, I can't simply reject these items through the constraint since they should still be available at this position, just not in the completion menu.