Assuming this is not to be permanent fixing and you will be removing/moving it on a regular basis, a bit of DIY will sort it.
Couple of heavy duty crocodile clips - as used on car battery jump leads - and a connecting shaft between them
As there's virtually no weight in the plate and aerial, a length of stiff plastic, aluminium, wood or whatever you've got lying about would suffice. If you need one clip horizontal and the other vertical then a right angled piece of metal.
Bit of scrounging needed :-)