1: Create a piano score in any key, except not in C major.
2: Put any note anywhere onto first staff.
3: Add trill mark to it.
4: Move it to the second staff by Ctrl+Shift+Down. It trills like in C major.
ie. if you have note E in D major, it trills like E-F, instead of E-F#. Or A in F major, it trills like A-B, instead of A-Bb.