You might find the add-on rather expensive as DTW-PPT anfd ORD-PPT fares may be much more than LAX-PPT fares. Several (6) years ago, I was looking for O/W fares to PPT. Turned out the cheapest AF fare was ex-SFO due to competition with UA's and BF's n/s flights. The n/s from LAX was only slightly more expensive and probably kept in check by competition with TN. Fares from SEA and YVR were significantly more (IIRC 3-4x more), even if the TPAC was the particular, cheap date AF flight. I checked fares though AF (where I ultimately purchased the tickets) and, IIRC, DL.