Non-rectangular base lots, what are the possibilities

[Trias]

I'm pretty new to the scene so please excuse my possible ignorance.

In the game pretty much all lots have a rectangular base.
I was wondering if there is any way around this. Could you create custom lots that have any irregular shape base? Would it be possible to create a lot that is shaped like an L, or something?

The main reason I'm asking is an annoyance I have when using roundabouts. Roundabouts rock, but take a way a single tile from an otherwise straight corner. This poses a problem when you want to place a large lot (such as a university) in a corner with a roundabout, cause it will basically waste a large 1xN strip of land. (of course you can sometimes make use of this land, but many times you cant.) It would be awesome if there exist puzzle pieces that snugly fit into a corner with a roundabout.

[Godzillaman]

Due to game limitations, I don't believe that there can be any irregular shaped lots. However, the building can be overhanging to get around this.