Thanks Brian!
Thanks to you I've been able to made SH3D to print pdf at any size (from Custom thru A0, Letter, Engineering B~E, Arch B~E to Envelop).
That's the good news.
The bad news (for you) I've done this under linux but you could find a similar solution for apple.

Under linux install printer-driver-cups-pdf pakage.
This will add an PDF printer virtual device to the system.
Make it default.
Now, under SH3D you will have all possible paper sizes.