These are all great answers, and I know i'm posting really late, but you don't have to do this, it's much too complicated. I do this:
First, I apply a stroke effect to the layer via Blending Options.
From there, all I have to do is drag the fill bar at the bottom right to 0%.
It may not be as pretty or accurate as the other answers, but it is definitely ...
Sorry for the tardy response, took awhile to work through this.
Using "method two" from Billy Kerr succeeded after changing the "near-white" to "f7f7f7". Finding the whitest successful value required some experimentation - i.e. the slightly whiter "fafafa" did not work, again giving transparent areas (for 32 colors - ...
As far as I know, there's no way to get Inkscape to do it the way you suggest. When you use the "remove background" option, Inkscape can't tell the difference between white and transparent.
Here are a couple of simple workarounds:
Trace as you would normally, using the "remove background" option.
After the trace, draw a white filled ...