The licensed versions of UBB do support defaults for that value.
The freeware version hasn't been available for download since UBB6.0 was publicly released though - I doubt it is still supported. There is a UBB6 demo version which you can download, but it is a DEMO, and it too is not fully functional. (Though you see most of the CP options - they're just not active, amongst other restrictions)
I would suggest reading
this page for a detailed description of the UBB6 demo.
Graeme