Depends on the input resistance of this MEMS (is it linear? I have never used one), but you could use maybe a resistor and a variable voltage source to create the necessary current values.
The voltage source needs negative value too, with dual supply it is easy. If you don't have dual supply maybe a bridge-circuit from stereo potentiometer or a differentially variable voltage source could solve it.
It would help I think if you shared more data about the MEMS and your application, how accurate tuning you need, etc.