Outline (inward) with multiply option (or any other blend option)

I would like to use outline fx but with multiply blend option so that the outline isn’t just a solid color but derives from the sprite’s detail.

I was wondering if this will be possible?

I was looking at the convolution matrix, and then possibly add one there… but don’t know how to add custom ones.

Make your outline with the outline fx, make sure it’s a color that isn’t anywhere else in your image, then use the magic wand to select the entire outline, by unchecking the “contiguous” box, copy it, then undo until the outline is gone again, make a new layer, paste the outline there.

After that just press F1 to access the layer blend options and pick whichever you want.