This discussion has some tips for the query strings: https://forum.inaturalist.org/t/how-to-use-inaturalists-search-urls-wiki/63
Any of the urls that start with "https://www.inaturalist.org/observations?" should work in the compare tool, just use everything that appears after the “?” For example “https://www.inaturalist.org/observations?taxon_ids=85553,26039,47113&place_id=7613,10301” would be taxon_ids=85553,26039,47113&place_id=7613,10301 in the compare query.