Formatter has quite a few extensions to allow a forced page count. The xsl-fo standard only allows 'auto | even | odd | end-on-even | end-on-odd | no-force | inherit' as values for the 'force-page-count' property but Formatter allows integer values, multiple + offset values, and an option to base the count on physical document pages. See C:/Program Files/Antenna House/AHFormatterV65/docs/ahf-ext.html#axf.force-page-count for more details.
Forced page count sample. In the samples all the flows are put into their own fo:page-sequences and for the blank pages the force-page-count extensions are used:
<!-- blank pages pad -->
<fo:page-sequence master-reference="simpleExample" font-family="Times"
That will pad based on the physical page numbers allowing page number resets in the previous sequences. This also uses the Formatter extension of allowing empty page sequences (without fo:flow elements). That allows it to possibly generate 0 pages if the cover and content already fill 23 pages.