Does anyone know of a possible solution to adapt, convert or add an RF wireless unit to a Harmony One remote?

There are replacement batteries for other remotes from NGHP which have an RF capability built in, however the Harmony One uses a flat battery pack like some mobile phones.

Barring that does anyone know of an IR to RF extender? (Not IR to RF because that won't help)

Cheers...

The Harmony One remote is strictly IR and will not work with the RF extender. As far as the batteries their are Mobil Phone batteries that will work in the Harmony remote but are not able to be recharged while in the Harmony remote. There are nor RF adapter batteries that will work with any of the Harmony rechargeable remotes

If you have wire access you can use an IR repeater - they work great. If you want wireless just get a wireless IR to IR repeater - no wires needed.