,Once issued the Certificate under 61.75 functions like any other Pilot Certificate - a current Flight Review* or acceptable alternative is required. This must be done by an "authorized instructor" (AKA FAA CFI). 90-day currency does not have to be N-reg.
I doubt that any FAA Civil Servant would sign off someone's Wings flights without knowing all the people involved, though that would indeed count towards one of 61.56's alternatives. (Wings requires three flight credits and three online training credits, then resets the Flight Review for 24 more calendar months. I think it's a great program!)
This is sort of a moot point anyway. No one is going to rent an airplane to a stranger without a thorough checkout. This will certainly cover the flying portion of a Flight Review. The ground portion is an hour of review of FARs which is valuable for someone about to use their FAA Certificate for the first time.
The FAA's website gives a good overview of the process. Apply, indicating which FSDO you want to use. Have the CAA validate your license. Wait patiently throughout the process. IIRC the webpage suggests allowing 90 days.
In addition to a current Flight Review, a valid Medical is required. I don't believe an EASA Medical is accepted for use with an FAA certificate. I know I was not able to use my Second Class FAA Medical to fly in Germany on my EASA PPL last Autumn. (Although it was acceptable to extend my SEP rating last month with the German Authorities).
It may look like there are a lot of moving parts to make the 61.75 piggy back Certificate work, it's much easier than going the other way! Many, many people have done this and had a great time flying.
Good luck
Terry
Hasn't been a "BFR" since 1997...