Oobie, I know that this sounds tacky, but we have done it out of desperation.
Years ago, we sold Comdial Solo II phones that had a power cord that consisted of 24/2 parallel wire (similar to lamp cord but smaller). They had a 6P2C plug on the end that connected to the phone. We often had to extend these beyond the 7' reach of the power cord.
We used clear 24/2 speaker wire and tinned the stripped the ends. They fit perfectly into the channels in the mod plugs. Regardless of solid or stranded type plugs, there was enough of a bite to make the connection.
It is a lot of work, but they look like real cords when you are finished. You just have to feel like just sitting down for a few hours and making some up.
I wish I had a better solution, but I haven't seen one yet.
