Hi,

Same problem when the TV remote controls were introduced.
To replace the potentiometers, ICs + fixed value resistors
were used.

From the 4000 Series CMOS:

Quad Bilateral Switches
4016, 4066.

CMOS Analog Multiplexers/Demultiplexers
4051, 4052, 4053.

* * *

About the 4016:
http://www.doctronics.co.uk/4016.htm

* * *

Modern Digital Potentiometers:
http://www.maxim-ic.com/DigitalPotentiometers.cfm

Best regards,

Luciano