If you have to cut it to make it work, flip it to the passenger side, cut it there, and put the filter over there where the battery traditionally goes.
Then if you need to add a bit of sheet metal to the area, you can, and it only gets into your passengers seating area. I need my seat all the way back in my 914s. My passengers are normally compact than I.
You could also cut the tube and use a silicone tube to fit and then make your transition to the Air tube.
Or fabricate an new TB opening duct, and make it fit a bit better.
Another option is cut a notch in the duct and plastic weld a notch in it. Or find a section of plastic tube from another intake that goes oolong to allow the same area of airflow to pass thru, and plastic weld it up and in.
This is after the MAF so it will need to be sealed.
For east=y no car cutting method you can do at home.
I thought about making one out of carbon or fiberglass fiber prepreg tape. make the piece out of foam, wrap it in plastic tape, wrap the prepreg around my now buck, and you can clean it up if you want or leave it. Pretty easy and comes in all sorts of neon colors or white if you want.
Example skip past the intro but you get an idea of how you can use this to your advantage. Use foam as it is easier than doing this in metal tubing and then doing like they did in the video. Foam you can jut bust it out in pieces to get it out of the tube.