I actually have a PhD in molecular biology--but in an area of study totally unrelated to this topic. Overall, I would have to believe that it would be FAR more involved than EITHER outright synthesis (even if you had to work on synthesizing some of the precursors on your own) OR (of course) extracting it from plants.

To begin, you'd want to have some quick and easy (and cheap) assay available for the presence of DMT. I don't think there is one, now, is there? If you had that, you could try for some "thrown it in and hope" transformations, and over time hope to select for a clone that had good production.

If I had a good and simple assay though, I'd instead use it for testing indigenous plants for new extraction targets.

Thinking about such things is MUCH easier than trying to carry it out in the lab--it's a LOT OF WORK!