You can't do page (A4) within a page (driver page size) automatically so you'll have to create layouts for that:

• Scroll to the bottom of the thumbs and add the "Template" thumbnail at a size of A4: repeat as many times as you like (each template will be an A4 page)
• You can only get two A4 pages across the width of a 24 inch roll so you might as well put them on landscape if you want to optimize paper use
• Once all your A4 template "pages" have been placed, select them all on the live view and add an 8 inch white border: that will turn the pages into white mats
• Select "Freehand" placement under the live view so you can manually place templates (below) for the prints
• Now you can select the same "Template" thumbnail and add as many print sizes as you want and drag them on top of the A4 mats to create "cells" on those "pages"

(make sure you clear that 8 inch white border as you want regular templates now, not mats)

• Once you are done, drop down the placement button below the live view, select "Save Current as Custom Layout" and give it a name

Whenever you want to use that custom layout, just drop down that same placement option and load the layout by name.  My suggestion would be to create two landscape A4 size mats which will use up about 23 inches of the width of the roll and set your paper length (in the driver) so that it is just long enough for those two pages.  When you save/open the layout and start adding photos, they will populate the red templates on top of the A4 mats automatically, row by row.

You can easily see where to cut the A4 pages too: drop down cut marks and select something like corner marks: it'll only mark the corners of those A4 mats.

Edit: added an example screenshot where I created two A4 pages with one 5x7 and one 4x6 on each page.

Regards,
Mike