Control 'indexability' from within EE

I have a client who wants to use ExpressionEngine to create a series of specific landing pages, this is simple. However they are asking for the ability to specify from within the CMS whether to not the page should be indexed by Google etc.

Ordinarily, I would do this via the robots.txt file, but i’m pretty sure EE can’t write new values to this…

Any other obviously ways to accomplish this? Maybe a plugin I’m not aware of - I can’t seem to find anything.

Thanks

R