To revalidate the UK SEP - I don't want to be EASA'd - can I simply get freelance refresher instruction in the Kitfox and then when he thinks I'm OK, a proficiency check in the Kitfox with an Examiner, he signs the revalidation and that's it?
The requirement for ATO involvement for renewal of class ratings in EASA licences is derived from FCL.740(b) and the associated AMC.
A requirement for ATO involvement is not contained within national regulation, so does not apply to a class rating contained in a national PPL (ie. UK PPL) or National PPL (NPPL). The text which precedes Table 1 in the ANO explains this (see ANO page 204
Therefore, the answer to your question is YES: for renewal of your SEP class rating in your UK PPL, it's just training as required with a suitably qualified instructor plus a SEP Proficiency Check with an examiner. Providing the class rating is in Section XII of your licence, the examiner can then sign your Certificate of Revalidation and complete the paperwork to send in to the CAA.
The LAA Pilot Coaching Scheme is a Registered Facility so can conduct renewal training for EASA licences; a number of LAA coaches are also examiners. See LAA coach map here: http://www.tinyurl.com/laacoach