Folder size exclude an ext

Proprably impossible but i'll try to ask.

There is an API, WMI or any other things that give me a folder size but with a filter, so excluding an extension of a file? Like take this folder ( and his subfolder ) give me the size without any .word file.

I know i can search all the file, exclude the .word, loop all the file with FileGetSize and finally sum the total size but if exist a faster way please tell me.

Thank you