ConversionTrackerService.mutate() with operation ADD. Is that what you mean?
Assuming you not only want to create new conversion types, but also update certain webpages to register conversions of the new type:
After creating the conversiontracker, retrieve it again, then use AdWordsConversionTracker.snippet (a property) to get a conversion script. Unfortunately, the individual conversiontracker ID to use in webpages is not available separately, the only way to get it is to parse AdWordsConversionTracker.snippet - and hope Google never changes its structure.
Hope this helps.