The only way I know of is by manually changing the cut-out. This can be done by importing your window in a furniture library using the
Furniture Library Editor. Using that editor you can modify the cut-out which is defined by a SVG path.

This Guide for SVG Path cut-outs by OKH is very helpful to get to understand how to do that. It should be possible to have multiple cut-outs before the closing "z" in the SVG path definition but you might have to read a few other sources about SVG paths.