This is only possible if the Nova is used in Performance Mode. To do this :

(1) Select the Part using the Arpeggiator in question.

(2) In the Range Menu, adjust the Part's note range so that only the
desired keyboard keys trigger the arpeggiator.

(3) If required, in the Tune Menu, adjust the Part's tuning, so that the
arpeggiator is played back at the desired musical pitch.

(4) If a polyphonic arp pattern is being used, it may be useful to turn the
'Constant pitch' parameter (in the Arp Menu) to 'On'. If this is done, when
the pattern is triggered, it will always play in the same musical 'key'
regardless of which keyboard note triggered it. (In the poly pattern data,
a note transpose value of +00 is presumed to represent 'Middle C').