In that case I would try to arrange for having naloxone around next time. The way and relative rapidity with which fentanyl is metabolised and eliminated and IV fentanyl is absorbed and distributed means that there are not, to the best of my knowledge, anything like the lemon juice/Vitamin C methods for quickening methadone elimination. I do not think slapping the person or putting them in the shower is going to be as effective as it may be with other things, though if it was fentanyl by itself, keeping the person awake is a difficult and labour-intensive process which requires constant attention but it may only need to be done for 45-120 minutes depending on dose and other factors. I hope that no one thinks that an intra-cardiac injection of milk can do the trick. But medical attention is imperative, usually hospital/EMT, or if a trained and knowledgeable person is around and there is naloxone on hand, that may do it but close monitoring is essential.
The same would go for getting too much through the mucous membranes -- but if one likes fentanyl or sufentanil lozenges and lollypops, tape the lollypops to your hand so when you get enough for a hard nod it falls out of your mouth and does not overdose you. The Danish military I believe invented this for their medics to use on the battlefield and now lots of nations and organisations do it.
Fentanyl effervescent tablets -- start slow as one can always take more later not less.
For the Duragesic/Durogesic/Chronogesic using folks out there, one thing which you must watch out for applying too many, as if they are clinically effective for their labelled purpose, that means that the skin below the patch has developed a bolus of fentanyl or sufentanil which can create therapeutic or supratherapeutic plasma concentrations of fentanyl/sufentanil for up to 17 hours or more. Again, then it is naloxone time and if one patch is delivering too much, one can always put the bottom plastic piece that was removed to expose the adhesive on the adhesive side of the patch to expose a fraction of the surface area to reduce the fentanyl delivery rate and make the patch last longer -- just move the plastic and expose the covered and vice versa area later. Kick-starting them with a heating pad, well one has to do what they have to do in pain, but do like the lollypop medics and sit on an edge of a chair so you will fall down and drop the heating pad if you fall asleep/nod/pass out.
If one uses patches in a manner inconsistent with their labelling, have plenty of naloxone on hand.