afaik you can't. Which is bad.
But the latest versions of the MBS Plugin place a copy script button on your script window, once you click it you can paste the script in a WP and format it as you like. Which is good.
(Very long script lines do have problems, though, they get truncated + a "...]" at the end):
Set Variable [$$mysql2; Value:Let ([ mysql = "SELECT SUM(PartialAmountPaid) FROM PaymentSQL WHERE "; type =Char(34) & "Bill status" & Char(34) & " = " & Char(39) & "Partially closed" & Char(39); role = If(Bill::gCV_Role = "Owner"; Char(34) & "…]
and that is bad, again, but with normal line-length scripts you should be ok.
If you have a Mac, you can use TextMate, which has an excellent Filemaker plugin. It allows you to copy/paste without the length limitation you mentioned. I use it for editing scripts sometimes. The syntax of pasted scripts is pretty archaic, though, so it's not a great workaround for printing.