Yes I was a little disappointed too but it is a bit far out there so scepticism is quite understandable.

Breeding would be a much nicer option, both DMT and gramine expression is highly variable so it would likely be quite quick and easy to selectively breed it. Hybridization might even break the gramine pathway completely since P. uses different enzymes to produce it, although GM would be a much faster way to that if you had the lab for it.

If you planted gramine-free phalaris outdoors you would want to prevent it from seeding itself though since grass pollen travels so far, and producing seed for that would probably have to be done in a glasshouse which would be a bit of a bother but certainly worth it. The initial breeding could be done anywhere though since you are testing it. I would really look forward to this though since once it is done it would be very easy for folks to grow and extract without much difficulty or risk.

I did a bit more research and it looks like the conversion would not be fast enough to be completed in a day, but would certainly produce DMT faster than would occur in the same quantity of the phalaris you extracted the enzymes from. To counter the slow speed you could heat it up as far as it will go without cooking the enzymes, add some easily removable preservatives, and leave it sitting in a cupboard for a couple of weeks and probably end up with more DMT than you know what to do with.

The main thing that I think could be a source of complication is the preservatives that you may need for long incubation, many methods are available for this but hopefully the most basic methods or even doing nothing at all will suffice. I would need to find someone who knows a lot more to find out if I've overlooked something though and would need to actually do it to find out if there was something more subtle missing.