Place a fence post where you want your lever to be placed

Place an item frame on it

And a second one, like this

Place the first carpet on the frame

And, while standing in the middle of the item frames, place the second carpet

Without moving, keep right-clicking to rotate it

Until in«t's in the desired position

Break the fence post and quickly place another block in the same place, before the item frames break

Finally, place the lever outside the item frame

That's it! Thanks for reading!