A tune will certainly make a very noticable difference in midrange torqu and power available for a given throttle input. The beauty of the Trifecta tune is "select-a-tune" that allows you to switch between an ECO and Power tune via the cruise control button (or stock tune & power tune if you request it).
So depending on how you request you tune, pusing the cruise on/off button (you don't actually have to have the cruise set) will swap between the the power and eco tune. As long as your wife isn't on the power tune she will be none the wiser.
Depending on how your wife drives ie. If she drives with the cruise on all the time then set you tune with ECO tune on when cruise is on (this is defualt from trifecta)
If she only activates cruise control when she actually engages the cruise or never uses it then get the Tune set up for ECO or Stock with cruise off.
If either of those options sounds like it would work then she will be none the wiser. As an added plus you will have a huge grin everytime you drive because all the extra power
-tyler