Port ranges and rdr

[Jonas Carlsson]

I'd like to store a list of ports and portranges in a variable called, 
lets say $ports_to_rdr
and then:

rdr on $ext_if inet proto tcp from any to ($ext_if) port $ports_to_rdr 
-> $server
pass in on $ext_if inet proto tcp from any to $server port $ports_to_rdr 
flags S/SA modulate state

but however i try to define $ports_to_rdr pfctl wont accept my ruleset. 
I think the manpage said
"rdr" and "pass" have different syntax for port-ranges, but this seems 
very strange to me?!

howevery, since i want to be flexible with which ports i redirect,
how do i solve this without using a million of rules and specifying all 
ports manually?