I just bought a "eKit 4 in 1 Connection Kit for Samsung Galaxy S3 / S2 / Galaxy Note"
http://www.amazon.co.uk/eKit-Connect.../dp/B006I31SHC
and have now a working SD-slot for my Nexus 7. I actually have both SD and micro-SD and USB. Works very well with Nexus Media Importer. The only disadvantage is the that the connector is a bit loose so you have to be careful to ensure that it is plugged in properly. For watching videos at vaccations I see no disadvantage with this approach.