Either that or I'm wrong and will look silly for the first time in my life.
Why not take advantage of the fact that so many things make the BBB fail the PWP and engineer a temporary BBB "failure" to coincide with a peak in the curve of L-dopa or mucuna or whatever that you are trying to deliver into the brain?
Example: Assume that sugar makes it permeable for an hour. And assume that mucuna triggers an increase in dopamine production. Fiddle with the timing to get the two Tmax events to coincide.
Too much trial and error for a few white rats but it is worth thinking about.