ignore classes of files for completion on a per directory basis?

["sam reckoner" <sam.reckoner@xxxxxxxxx>]

I would like to setup completion to ignore a certain group of files
(say, those with an underscore in the file names) when I am trying to
complete when in a specific directory. What makes this tricky is that
I may not want those same filenames (those with underscores in them)
in a neighboring subdirectory to be ignored for completion.

I know it's possible to configure completion to ignore a pattern of
filenames globally, but how about on a per-directory basis?

thanks in advance.