SuperSpice .subckt and variable

I want my subcircuit to have variable/parameter/value. Something like every resistor has resistance.. So, when I draw schematics, its very easy to change resistor value and each and every resistor can have different value. I want that same thing for my .subckt and not to have to make different model for every possible value.

for eg. this is what i got and it works real nice:

..SUBCKT KP_XN _ssi_pin0 2

• _SS_Symbol [C:\Program Files\AnaSoft\SuperSpice\System\SchematicBlocks.ssm] [2PinBlock] B1 _ssi_pin0 2 I=13.5/V(_ssi_pin0,2) ..ENDS

but I wish for something like this:

..SUBCKT KP_XN _ssi_pin0 2

• _SS_Symbol [C:\Program Files\AnaSoft\SuperSpice\System\SchematicBlocks.ssm] [2PinBlock] B1 _ssi_pin0 2 I=a/V(_ssi_pin0,2) ..ENDS

and to be able to change value of a when drawing schematics the same way I change value of ordinary resistor. Is it possible?

TIA