Hello Thorsten,
I don't think that is possible without a hack (eg. putting a blank div on top of your player).
I do think however that this practise will ruin you UX.
Imagine users clicking on the vid and getting no reaction, plus you will make your page unnecessary heavy.
You should use a service
like this
for thumbails and extrafields to display these images.
I hope that was helpfull to you.