> I was told that Interleaf has this feature and it works well, but I've not used that program myself.
You'll need to be cautious about that advice. Interleaf, per se, hasn't been available under that name for some 14 years now.
Interleaf was rebranded as QuickSilver shortly after the 2000 acquisition by BroadVision.
Given that FM's Freeze Pages feature converts what is usually a monolithic flow into disconnected pages, I think if I had to support a document like that, I'd make each page a separate file (chapter), and let each file have a normal connected flow with an "X.#" page numbering in the footer, where X might come in from the file name, a variable, a cross-reference or simply be hand-typed.