Dancing in spikes - Don't know of software but sounds an ideal solution.
One way to get rid of the unwanted laps is to go to your forerunner and go to 'history' , 'activities' and select the activity you want to edit. You can then scroll through all the laps and when you get to the ones you want to get rid of press 'clear' (bottom button) it will then ask you to confirm you want to delete this lap.
You can then go to garmin connect and delete the workout you want to change and then upload the corrected version. I had to do a force send from the forerunner (settings - ANT+ and turn on force send).
Hope that helps.