Is it possible to use URL Rewrite to provide more complex query string functionality than the "Append query string" checkbox that it has? Specifically, is it possible to specify the keys for certain query string parameters and have it only append those name value pairs.

For example, for the input:

http://www.example.org/test?alpha=1&beta=2&gamma=3

and the list of query string parameter keys: beta gamma

it should output: http://www.example.org/redirect?beta=2&gamma=3

(Note that the query string parameters in the input appear in arbitrary order.)