14 CFR 61.57 Recency of experience
It does NOT state anywhere that you need to use an N-reg for any form of currency. It specifically states:
(c) Instrument experience. Except as provided in paragraph (e) of this section, a person may act as pilot in command under IFR or weather conditions less than the minimums prescribed for VFR only if:
(1) Use of an airplane, powered-lift, helicopter, or airship for maintaining instrument experience. Within the 6 calendar months preceding the month of the flight, that person performed and logged at least the following tasks and iterations in an airplane, powered-lift, helicopter, or airship, as appropriate, for the instrument rating privileges to be maintained in actual weather conditions, or under simulated conditions using a view-limiting device that involves having performed the following—
(i) Six instrument approaches.
(ii) Holding procedures and tasks.
(iii) Intercepting and tracking courses through the use of navigational electronic systems.
I have never heard of any FAA requirement that needs to be completed in an N-reg. Yes, you need to use a FAA CFII for an IPC but if you are still within your second 6 months you can use any (at least) private pilot as a safety pilot to make yourself current again.
A N-reg is not even required for a check ride if the examiner approves:
14 CFR 61.45:
(2) At the discretion of the examiner who administers the practical test, the applicant may furnish—
(i) An aircraft that has an airworthiness certificate other than a standard airworthiness certificate or special airworthiness certificate in the limited, primary, or light-sport category, but that otherwise meets the requirements of paragraph (a)(1) of this section;
(ii) An aircraft of the same category, class, and type, if applicable, of foreign registry that is properly certificated by the country of registry;
In short, you're safe by doing recurrency in another registry.