led dimmer lamp retrofit
Dimmers of the type that go inside lamps (are we talking a halogen torchiere here?) are commodity components, and generally do not take a neutral.  

One option is to go with low voltage (12-24V) LEDs e.g. LED strips, and use the technology used to dim those -- PWM.  You may be able to find a PWM dimmer with a rheostat input, and  relocate the rheostat (or one of equivalent value) to the standard location.  This kind of hacking and experimentation is much more appropriate with low voltage lighting, where the risk of electrical shock is off the table.