ADDENDUM:
I have used Bertrand Le Roy's code (make that Pete Hurst's code) and created a module with it, then added 3 content parts that are all copies of the bodypart in Core/Common.
In the same module I have created a ContentType and added my three custom ContentParts to it, plus autoroute and bodypart and tags, etc, everything to make it just like the Orchard Pages ContentType, only with more Parts, each with their own shape.
I have called my ContentType a View.
So you can now create pages for your site using Views. You then use the ZoneProxy to shunt the custom ContentPart shapes (Parts_MainImage, Parts_RightContent, Parts_LeftContent) into whatever Zones I need them in. And job done.
Not quite Sitefinity, but as Bill would say, Good enough.
The reason you have to create your own ContentParts that copy BodyPart instead of just using a TextField, is that all TextFields have the same Shape, so if you use ZoneProxy to place them, they all end up in the same Zone. Ie, you build the custom ContentParts JUST so that you get the Shapes. Cos it is the shapes that you place with the ZoneProxy code.
Once I have tested this, I will upload it as a module onto the Orchard Gallery. It will be called Wingspan.Views.
I am away on holiday until 12th June 2012, so don't expect it before the end of the month.
But essentially, with Pete Hurst's code, that is how I have solved my problem.
EDIT:
I could have got the same results by just creating the three content parts (LeftContent, RightContent, MainImage, etc), or whatever content parts are needed, and then adding them to the Page content type.
That way, you only add what is needed.
However, there is some advantage in having a standard ContentType that can be just used out of the box.
Using placement (Placement.info file) you could use the MainImage content part for a footer, for example. Ie, the names should probably be part 1, part 2, etc.
None of this would be necessary if there was a way of giving the shape produced by the TextField a custom name. That way, you could add as may TextFields as you liked, and then place them using the ZoneProxy code. I'm not sure if this would be possible.