Food tracking, without the sauce.

Since no one else has answered: I'm assuming your packaged doesn't break it out. I've seen some that list the sauce separately, or list as "Prepared with" and "prepared without" or some variation on that theme.

About the only other option I can think of is to estimate the amount of sauce (if it's not printed somewhere on the package), find a middling-calorie estimate for a similar sauce in the database, and subtract that many calories. You could subtract it by creating your own food in the database with the lower calories/nutrients, or (though this would distort things a little in other ways, create a fake exercise entry for that many calories.

It's a little more complicated, but you could find a similar sauce that's sold separately and subtract the calories and macros. On the desktop version of MFP you can log negative portions.