I see that the composite isn't managed directly as a font in the tool. Instead the tool only creates a bit-map for composites, which isn't a terrible choice; the target for pasting will likely be a picture so you could just use a bitmap editor to duplicate the top datum feature references. There are fragment characters to handle the composite system; you can see them in the tool by selecting "..." so you can compose them directly if you like.
With more experimentation, either Windows or TrueType seems to have a basic limitation on how it handles fonts and apparently demands at least one pixel vertical spacing between lines. I tried Word, Notepad, and Wordpad, with the closest shot being Notepad. Attempts to close the gap with line spacing in Word caused vertical truncation; Wordpad seemed to not recognize the double-byte characters correctly at all though maybe there is a setting somewhere.
The best result was in Inkscape where I could create separate top and bottom text segments and just align them. Obviously the same would happen in a bitmap editor. Inkscape also had a small vertical gap between the upper and lower segments when they were in a single, two line text block, which is why I wonder if it's a TrueType problem.
In the past I have found that single-line stroke fonts are not possible in TrueType, which requires a boundary that is filled. This flaw means that TrueType fonts are not good candidates for single-cut engraving. It's possible in the bitmap generation for screen display that the default is to generate a blank background, marking pixels and stamping the whole thing, instead of ANDing the marked pixels with the target area.
I expect that's why someone (Peter Kanold) who went to the trouble to create a font and a tool to use it did not bother creating a character-based output for multi-line FCFs.
