Mini-blinds can be shortened so their overall height is less, and usually the slats can be cut to a slightly shorter length as well, depending on what they're made of. You might be able to shorten some of the slats that go beside the AC and still have them in the blind. A lot depends on how many cords you have that go down through the blind (for example, how wide is the blind?), and how many of those cords are in the blinds beside the AC. Then even if you shorten some of the slats, you'd still have to figure out how to have the heavy bottom rail divided into 2 lengths. Possibly can be cut, but you'd need something to finish off the ends of it at each height. I'm sorry I don't have time to draw a diagram, but if you've shortened any of yours, you may understand what I mean. Good luck!

Probably you should try the curtain designs given here.
http://www.dekornation.com/curtains-and-cushions-drapery-linen/curtains.html
http://www.dekornation.com/curtains-and-cushions-drapery-linen/customized-cushions.html
http://www.dekornation.com/curtains-and-cushions-drapery-linen/linen-pillows-blankets-throws-bedsheet-sets.html

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Damn spammers!

I understand what sujafr is suggesting, but at a minimum you would need two vertical cords to hold up the cut blind.

Can you share a picture of the room with the window in view so we can get a real idea of what it looks like?

Are you trying to cover the accordion-like pleated vinyl that usually extends on either side of the AC unit to close off the window opening?

I have bamboo-type shades in my office, and in the summer when I put the AC in the window, I lower the shade to the top of the AC and have total privacy at that window, if that is the goal.

I see you said 'cover the bare window beside the AC'. Could you find a fabric close to the color of the mini blinds and attach it to the bottom of the blind on either side of the AC?