I pressed them down straight as possible onto the stem.
I assume you're looking for 1U labeled stuff thats the correct row sculpt and things like that.. yes it would be difficult with out buying a "planck" add-on set or something that was specific to the weird setups.
Another option would be to buy all 'row 3' caps. I know you can buy them individually
here but there was another website in England that had some sets also but I cant think of it. Maybe someone else will post it up.