There is a kit called a spanner flange. It's just a slice of metal with an oval cutout for the bolt. It slides underneath your flange. I'ved used them in quick temporary fixes but as a plumber I can't warranty that so it's not something I would do on a job. As far as your bolts being nutted underneath that's not very likely but I suppose there's no telling what someone may have done in recent years. If you decide to tackle this project and do a thourough repair I think you'll be more satisfied and sleep a little easier when done. Once you open the ceiling,wall, or wherever that pipe may fall I think you will find it's not as difficult as it seems. Here is a link for the spanner flange.http://www.cornerhardware.com/hardware/Plumbing/Toilet_Repair_Parts/Mounting_Bolts_Parts-536.html
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