Blackout roller blinds over 90 degree

[NotPracticalAl]

First post from a not hugely practical but enthusiastic soon to be father desperately trying to get the house ready for the new arrival. Hopefully the first of many on here in search for help, who knows, maybe I'll one day be able to help someone else out, I'm pretty handy with a Sky+ box...

Problem I have is the nursery is at the top of a staircase (dangerous, I know...) so I have to black out downstairs too, which has two tall windows across a corner with a structural post jammed in the corner of them with not a lot of room to get roller blinds in, definitely not fitted in the conventional way.

That is the corner window, the structural post isnt that clear but this is a close up below

I've only got about 2 and a half inches of window frame to play with on either side - I thought maybe some sort of angle bracket, but there might not even be room for that given the height of the window will need a large blind.

Any smarter ideas I'm missing or alternative blackout ideas? The previous residents seem to have velcro'd some sort of panel across it but I'd rather avoid that (unless I'm being dumb and I'm going to need that to black them out even if I get rollers in)

Any suggestions gratefully received

Al

 

[foxhole]

Plenty of room to get roman blinds in lined with black out material, need no roller.