This tip has been a lifesaver so many times before that I'm surprised I don't hear of more people doing it. Maybe it's more common that I'm aware of? I'm sure we've all been in sessions where in spite of our best laid plans, someone is just a little too far away from their headphone amp and the kind of lead there never seem to be quite enough of is headphone extensions.
Headphone Extensions - Necessary Evil
Personally I'd be very happy to live in a world where headphone extension cables were unnecessary but despite the existence of excellent solutions which should negate their use, I still seem to need one more often than I'd like.
For many years I've had an old pair of DT100s - you can probably see how many years from the ragged appearance of them! I've wired these to an XLR F and kept an XLR M to 1/4" TRS "bodge lead" on the end. These extra connectors present no practical obstruction to their use, the short length of cable between the jack plug and the male XLR means there is negligible extra strain put on the headphone socket.
The advantage of this is that, while there often isn't a headphone extension lead available, there is always an XLR lead handy. Simply put a spare mic lead between the XLRs and you have your extension.
Wall Boxes - Approach With Caution
It doesn't end there. It is straightforward to repurpose a tie line to send from a headphone amp via installed cabling, plugging the headphones straight into the wall box. Just don't do this in someone else's studio - there could be phantom power or even speaker level outputs on XLR. Hopefully everyone reading this knows never to plug headphones in while wearing them - there are far too many nasty surprises out there!