"Enrich Data by Webservice with HTTP Header"

In the tutorial 'RapidMiner to enrich Gender data', the API does not require authentication:
http://namesorts.com/2014/04/23/rapidminer-to-enrich-gender-data/

But (say you would like to use Mashape or some other auth method) how do you specify an API Key HTTP Header in the RapidMiner Webservice operator?

Thanks!
Elian