ShowModalDialog Problem When String Too Long - Any Alternatives ?

I am displaying a modal dialog in JScript using window.showModalDialog
passing a long string as URL - i.e. it contains variables values just
like a Get request. Problem is that string is now tool long and
showModalDialog fails. I'm aware of the DialogArguments and passing an
object to receiver but this is no good for me as the receiver needs to
access the long string in server side code and so would not know
anything about the dialogArguments class. Can anyone suggest a way for
me to show the dialog as modal and at same time get the long string into
the dialog and have the string accessable from both server side code and
client side within the dialog recever file ?