As above, if you use two 6" Bahco adjustables you can do it in situ, one holding and tother adjusting.

If you are nervous stick one of those belts on the bonnet, some like them but protect your paintwork first.

2009 4/4 Henrietta
1999 Indigo Blue +8
2009 4/4 Sport Green prev
1993 Connaught Green +8 prev