" We don't want the status line to cause problems:
set laststatus=0
redraw!
let g:totalLines = &lines * 20
let middle = g:totalLines / 2
wincmd n
wincmd o
for i in range(1, g:totalLines)
	call setline(i, 'LINE ' . i)
endfor

exe string(middle)
normal zt
normal M

aboveleft vert new
for i in range(1, g:totalLines)
	call setline(i, 'line ' . i)
endfor
exe string(middle)
normal zt
normal M
setl scb

wincmd p

setl scb
wincmd w