Without knowing exactly what you are trying to do, I'm having a little trouble helping. I'm a little concerned that putting in conditional statements may introduce a discontinuity that you might not really want.
If you want something that depends on both V and I, you could certainly convert the I to a V using a CCVS, and then combine the two Vs with a two-input VCVS.
Also, consider using a voltage-controlled resistor. I found this equation
Rpure 3 4 'Rsh/mf*(l-dl)/(w-dw)*tfacp*(1+pvcp1*(tanh(pvcp2*abs(v(3,4)/(l-dl))+pvcp3)-tanh(
pvcp3)))'
in an HSpice model file.
HSpice certainly gives you enough rope to hang yourself.