Unfortunately you can't control the vibrato in the strings. They are passionate, sure, but the vibrato is real, and as such is recorded right in the samples. So until GPO-A, we've got to use the tools we've got.
Vibrato control (cc 17 along with aftertouch) works only in the wind instruments, like bassoon, clarinet, trumpet, trombone.
I can't help you in terms of Logic, but in Finale, click the MIDI tool and double-click on the staff to open up the MIDI edit window. Select the CC and choose 17. Then make a selection in the MIDI edit window and from the menu, select 'Set To.' Enter a value and you'll see the data now appear in the window. At least that's how I think you do it. Others might be able to expand, clarify or correct any errors I may have made. I honestly don't use Finale for MIDI, just to enter in the notes. Then I save it as a MIDI file and open it in Digital Performer to do my editing.