TrollDragon
Headphoneus Supremus
My answer was to your question of the 99s fitting in it's case with the cable attached or a suitable plug that would allow such... Cable makers would gladly build you a cable IF there were connectors available to meet your needs, but there are none available. Most headphones that have a recessed jack have them located on the bottom of the cup, not parallel to the side of the cup.AFAIK custom cable makers can use any connector that the customer desires, so they certainly can use similar connectors. The 99's aren't the only headphones with recessed connectors, and the plug itself is merely a 3.5mm TS. Here's an example of compatible connectors : https://www.ebay.com/i/113871193058?chn=ps
That linked cable would work if you don't mind a fair bit of the gold shaft and the shell sticking out, it kind of takes away from the aesthetics of the 99s IMHO.
They would look similar to these (not my picture). Like everything in this hobby, if it's acceptable to you then that's all that matters.