Hi Ammonfife, It needs to be built…To my knowledge, there is no such smartapp at the moment.
Although, it might be possible to do it thru Rule Machine.
Regards.
P.S. My Ecobee device can toogle your fan mode without any issue.
It’s available at my store:
http://www.maisonsecomatiq.com/#!store/tc3yr
And, come with many smartapps at my github: