it’s probably not the best solution, but in case anyone else has the same question i used a hidden embed.
<a rel="shadowbox;width=640;height=480" href="#video-01" title=""><img src="my-picture.jpg" alt="" width="640" height="480" class="" /></a>
<div id="video-01" style="display:none">
<embed src="https://v.wordpress.com/wp-content/plugins/video/flvplayer.swf?ver=1.21" width="640" height="480" flashvars="guid=......"></embed>
</div>
with the flashvars from videopress’ embed code.