Cram a varitone into any guitar or bass. CTS makes a nice potentiometer that is called a stacked pot. It isnt like most stereo double deck pots the stacked pot has a separate shaft for each pot so they work independently. There is a center shaft and an outer shaft one inside the other. So when you are dealing with a guitar or bass that has 1 volume and 1 tone and you dont want to drill any new holes you can use the stacked pot to combine volume and tone then you have room for the varitone. The stacked pot is available in 250k/250k, 250k/500k, and 500k/500k. Here is an example of one of my harnesses for a precision or a tele type of guitar.
Most often I use the 250K/500K since most often the people who are interested in a varitone are those who like a lot of tone and as well many variations of tone. I think they are referred to as tone junkies! :)The 500K pot I wire for the tone pot this gives you a little more than a 250K. Either way it is a simple fix and eliminates the need to drill holes in your expensive guitar or bass and still upgrade to more possibilities. I sell this harness complete and ready to install for $58. If you want to build one for yourself I also sell kits.