documentclass[twoside]{article}
usepackage{everypage}
usepackage{lipsum}
newcounter{technicalpage}
setcounter{technicalpage}{1}
AddEverypageHook{stepcounter{technicalpage}}
begin{document}
  pagenumbering{roman}%
  %On page 1 (even)
  This is intro stuff and the page counter will reset further down. Technically page thetechnicalpage.parlipsum
  pagenumbering{arabic}
  Claims to be page thepage, but is technically page thetechnicalpagespace and should, internally, be treated as such.
  % Should say page 1, as it is, but should be treated like even with regards to margins,
  % because it's technically the second page. So I want't article to consider
  % c@technicalpage as the counter for determining odd/even page.
end{document}