Making changes to the Modern Lines theme in Aperture

I've been using Aperture for a while and am at a stage where I would like to put a book together using the built in software. From the few online reviews I can find, it seems to be a very high quality service.

Modern Lines is the theme that works best for me, but as with all the themes, there are some layouts that leave a lot to be desired.

A good example of what I'm trying to achieve is to take the "4 up" page and instead of being four 6x4 landscape photos, make it more like 2 16x9 landscape photos and 2 6x4 portrait photos.

so from:

|-------|  |  |-------|
|       |  |  |       |
|-------|  |  |-------|
           |
-----------------------
           |
|-------|  |  |-------|
|       |  |  |       |
|-------|  |  |-------|

to:

|-----------|  |  |---|
|           |  |  |   |
|-----------|  |  |---|
               |
-----------------------
               |
|-----------|  |  |---|
|           |  |  |   |
|-----------|  |  |---|

This is easy enough to do with the actual photo boxes, but the grid lines between the photos just don't seem to be editable. I can scale the grid, but not re-size. Hoping someone can give me an idea on how to handle this situation or is it just a case of finding another tool/theme that can do this?

iPhoto seems to handle the situation with photos better (but not perfectly) by re-sizing the photo boxes to be the correct orientation, but I guess Aperture gives you much greater control over these things and so doesn't take care of this for you.

Update:

While this isn't exactly what I was after, this thread has some useful shortcuts that may enable me to use another theme. Modern lines is still the theme I would like to use so I would like to see this question answered so that I could use it.