get-visual-selection.vim

function! s:get_visual_selection()
  " Why is this not a built-in Vim script function?!
  let [lnum1, col1] = getpos("'<")[1:2]
  let [lnum2, col2] = getpos("'>")[1:2]
  let lines = getline(lnum1, lnum2)
  let lines[-1] = lines[-1][: col2 - (&selection == 'inclusive' ? 1 : 2)]
  let lines[0] = lines[0][col1 - 1:]
  return join(lines, "\n")
endfunction

We also used this:
:autocmd CursorMoved * :if mode() == 'v' | :call feedkeys("\<Esc>gv",'n') | :exe printf(':match CursorColumn /\V\<%s\>/', escape(Get_visual_selection(), '/\')) | :endif

(Likely you want to drop the word borders \< \> around the %s in the :match pattern.)

I'm not sure the feedkeys() does anything.

An easier workaround to the whole s:get_visual_selection() approach would be just yanking the selection. Drawback is that that could overwrite a users's register. (But you could backup and restore the register.)
:
call feedkeys("\"tygv",'n') […] escape(@t, '/\'))

It's well possible there's a bug in col2 - (&selection == 'inclusive' ? 1 : 2). In particular the script crashes at line borders, so I think this does a 'buffer underrun' – try to access an index < 0. (Overrun also thinkable.)

Good luck!