I would agree with astragalus - it's one ingredient, that's easy to get and you don't have to go through a doctor. Your co-worker could buy it online or swing by a health food store and find it most likely. He will need to be sure to use it as Buhner suggests - "3,000 mg daily for 30 days, 1,000 mg daily thereafter, indefinitely."
buhnerhealinglyme.com/herbs/recently-bitten/Astragalus has been what has kept me Lyme free this last year. I've had several ticks attach, and three different times I had bites that acted as if my immune system was on overdrive, so I credit astragalus to keeping me Lyme free this year.
There are other protocols you could suggest, but most of all we want him to not have to deal with the things we deal with - so my first suggestion is astragalus, as it's easy and inexpensive.
He could go to a doctor and try to get Doxy, but that usually ends up being a fight - and he needs treatment just as quickly as he can get it now, while the bacteria is contained in the rash.
I can't recommend essential oils simply because I don't know enough about
them. I haven't seen enough people with healing from them as I have from Buhner's either, so I hesitate. You need to recommend something that has a lot of success for a wide range of people.