Formic acid dissolves Nylon.  We use a Formic acid solution to dissolve nylon when performing fiber content analysis in the Textile Laboratory where I work.  Polyester, acrylic, cotton and rayon and most other fibers are not dissolved by Formic acid, so unless they are using nylon in the absorbent pads, they probably won't be damaged to the point of falling apart.   Nylon is a relatively expensive fiber- Polyester is much cheaper  and softer.  Most non-woven textiles are made from polyester for this reason.  (I think its unlikely that nylon is used in the pads, but not impossible.)
So, I'd say you are probably safe in trying these pads out as a formic acid dispenser.  The non- woven (And probably) polyester shells may be tough enough to stand up to bee mandibles for the time of treatment.  The inside material, if they do get to it, is usually rayon fibers, and an absorbent gel similar to that used in diapers, diaper doublers (Now thres another product to explore if the capacity of pads is not large enough.) and the commercially prepared Formic Acid treatment packs.  They'll just carry it out of the hive if they manage to get thru the outside layers.
That said, and having worked with Formic acid in the lab, with Fume Hoods and full protective equipment at my disposal, It's not something I'd want to play around with at home.  It's stinky, smelly stuff, and while it is miscible in water, it does not dissolve readily in water.  Thus we use acetone to rinse and clean the Formic acid off of our samples, and to make sure that our glasswear is clean.  Residue left behind concentrates as it dries and becomes even more corrosive than the diluted solution.
 I'll leave mixing up formic acid treatments to others.
Ellen
Mark wrote;

why not apply the acid into =
those super-slim women's panty liners they advertise, and because they =
aren't supposed to leak they cld facilitate a slow release of gas over =
the treatment period. just pop them on top of the topbars & let them go =
to work!!

the only possible downsides i cld think of were:

the acid may "corrode" the panty liners
the bees may eat the panty liners (like they do newspaper)

does anyone else have any thoughts/experience on this idea?

cheers, mark