Sideways I don't think so. It is likely that the refrigerant won't flow properly. The do make AC units for casement windows though they are more expensive and get high enough in price that you might as well consider a rooftop RV unit.
If you decide to go with a traditional low cost unit you can run the unit completely inside BUT you will have to create an air tight box to encase the outside part of the unit and connect a dryer type hose to the outside. It is not as big of a hole as an entire AC unit but it is another hole. You will also need a watertight tray with a drain to the outside to collect the condensate.
Is it possible? Sure many will atest and tell you their stories but you need to balance what you want with the amount of time and effort to make it happen.
Rob, thanks for the input. No to the sideways use of a portable AC. I figured as much, but, hey, it never hurts to ask.
I appreciate the input and will check into some of the mods people have done.
There is a portable AC unit made now that you don't mount into a window. I saw it. The price was $400, a bit steep considering I'll use the unit a couple of times a year.
I'll keep looking. Other comments?