Thank you for your inquiry.
I must profess ignorance in that I have never previously heard of either of the two practices ("wiping the needle" or "rinsing the syringe"). My literature search, as yours, was not productive in this regard. Thus, my opinion would be, based upon these observations, that there is no evidence in the literature to support either practice. In addition, I share the concerns expressed in your letter regarding "wiping needles."
In summary, I can find no evidence to support either of the practices that you mentioned, and would be worried about the practice of "wiping the needle" prior to the injection. I really cannot offer any specific advice as to how you should approach the "believers" who specifically request a "needle wipe." Until there is evidence, however, to support either of these techniques, I am afraid there can be no definitive answer as to whether the practices would be helpful.
I hope this information is of help to you, and thank you again for your inquiry.
Phil Lieberman, M.D.