Super, thanks for asking!

" Super, thanks for asking!
" Barry Arthur, Jan 8 2012

function! Superscript()
  let line = matchlist(strpart(getline('.'), 0, col('.')), '.*\[\(\d\+\)$')
  if len(line) != 0
    let num = line[1]
    return "\<c-w>\<c-w>".join(map(split(num, '\zs'), '"\<c-k>".v:val."S"'), '')
  else
    return ']'
  endif
endfunction

inoremap <expr> ] Superscript()