Hi Nats,
Sorry, didn't read your question fully!
I think it is possible to do what you want, but you are going to have to get tricky.
Personally, if there is only a couple in your building, I'd build individual shapes using the mesh tool and save them as dumb library parts in the correct orientation to SEO from the outer face of the wall. Patch the 2d view to get it to display on plan correctly.
If there are many in the building of differing size I'd be tempted to edit the library part to make it more intelligent and do some of the work for you. You could make it so you could adjust the width, height and splay angle parametrically and how it displays in 2d. More work but maybe useful in future jobs.
Maybe GS will add it to the window settings in a future version hopefully.
(I'd also like an empty door opening that you could set different reveal settings if they are reading this!
as I don't think you can turn off the actual frame and door currently)
The attached shows the original mesh and the library part SEOed from the wall. (I haven't bothered to patch the 2d.)
There are probably other (better?) ways of doing it as well, feel free to add them below anyone!