Couldn’t you use U+1D52 MODIFIER LETTER SMALL O? (I changed the subject line because the invisible letter proposal is not relevant to the question about a lacuna character.)
> I strongly support this. In our historical corpus of Polish > > http://korpusy.klf.uw.edu.pl/en/IMPACT_GT_2/ > > we have in particular words ending with 'COMBINING LATIN SMALL LETTER > O' (U+0366). > > We had to precede the character with NBSP as the vase, but to preserve > the correct segmentation into words we had to treat NBSP as a letter.
