Why do you need 2 websites for the same content?!? Just use the .com
For the keywords I monitor in Google.co.uk 10 out of the top 10 websites are on .com domains. Some are UK companies, some are international, but none of them use .co.uk and they are doing just fine. Also, none of them use geo-targeting either, i.e. those same websites show on Google.com without the "United Kingdom" added to the description.