How to run a script using Shell in the background?

[Bojsza]

I have an application where one of the button's contains a script using 
the Shell function.

The Shell function runs a command line argument against a user selected 
file.

If the user has selected a large file it takes a couple of hours for 
the Shell function to complete (this is normal time frame if the 
equivalent command line was done outside of Revolution).

The button with the command is pretty basic

on mouseUp
...
...
put Shell ("cmd and selected file") into fld outPut
end mouseUp

In this form the user cannot do anything else with the Revolution 
application (waiting for the script to complete).

Surely there is a way to have the Shell run in the background therefore 
allowing the user to do other things in the application?

Thanks,

Glen