Yes, I've used rectogesic whilst breastfeeding (though I only used it for 2 weeks as the headaches were crippling for me, and moved to diltiazem).
Incidentally, the diltiazem also says to not use when BFing on the box, but is safe.
The Breastfeeding Network lists loads of meds and states the various risks for BFing, and you can contact them about the ones that are not listed (as I did for the dilt).
HTHs
Edit:
Thought I'd reproduce the email I had about dilt, which also mentions the safety of nitro:
I am the pharmacist providing information on the safety of drugs in breastmilk and your email was forwarded to me.
We dont have any studies on the amount of diltiazem which passes into milk via anoheal. We do know that the tablets of this drug are safe and that
an alternative drug for anal fissures (glyceryl trinitrate) doesnt cause problems for breastfed babies. So putting these two facts together I think it is very unlikely to affect your baby. You may notice some hot flushes and palpitations yourself.
All patient information leaflets tend to say dont use as manufacturers are not required to take responsibility - as explained here
http://www.breastfeedingnetwork.org.uk/patient-information-leaflets.html Regards Wendy
Wendy Jones PhD MRPharmS
BfN Drugline Pharmacist
(My emphasis)