[scribus] Something similar to bleeds, but without duplicated areas?

[Christoph Bloch]

I'd like to cut existing A3 documents into 2 A4 pages each, in order for
them to be printable on ordinary A4 printers. However, in order to avoid
loss due to printer margins, I need:
a) bleeds, i.e. a duplicated margin where the page is cut into halves, OR
b) nicer: a printer margin on both A4 pages where the A3 page is cut into
halves - without duplicated areas.

Both solutions obviously have to include a slight scaling of the contents
because the additional space cannot exceed the A4 pages.

I know how to get a) (by changing the page format + adding inside bleeds),
but I don't find a way for b). Any ideas? Thanks a lot in advance!

Christoph