dkelly, here's your drug test reference: FAR 135.1(a)(5). (It's really too bad that 119.1(e)(2) doesn't point you to it)
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§ 135.1 Applicability.
(a) This part prescribes rules governing -
(5) Nonstop sightseeing flights for compensation or hire that begin and end at the same airport, and are conducted within a 25 statute mile radius of that airport; however, except for operations subject to SFAR 50-2, these operations, when conducted for compensation or hire, must comply only with §§ 135.249, 135.251, 135.253, 135.255, and 135.353.
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That list of rules that you have to comply with? Those are the drug and drug-testing rules.
BTW, the "dual controls" reg is 91.109. It's been interpreted to mean flight controls. But remember that the reg isn't everything. I can think of a couple of scenarios, especially when under IFR, where I wouldn't feel comfortable as a CFII if I couldn't get to the avionics.