LTSpice parametric subcircuit instances
The LTSpice manual gives an example of how to do this:

* calling a subcircuit
*
* This is the circuit
X1 in out 0 divider top=9K bot=1K
V1 in 0 pulse(0 1 0 .5m .5m 0 1m)

* This is the subcircuit
.subckt divider A B C
R1 A B {top}
R2 B C {bot}
.ends divider
.tran 3m
.end 


The full syntax is given as:

Syntax: Xxxx n1 n2 n3... &lt;subckt name&gt; [&lt;parameter&gt;=&lt;expression&gt;] 


The rules for writing expressions are given in the section of the manual on "arbitrary behavioral voltage and current sources".