This is very different from being paid as a member of the EC and the important thing is to have complete transparency. Put together a proposal of what you would do, how many hours a week you would spend and how much it would cost and make it very easy for the EC to dispense with your services if they are unhappy at any time.
Make your case to the EC but then absent yourself from the meeting when this is being discussed and voted on (as a matter of courtesy, rather than any legal requirement) and let the committee decide.
If they say yes, then if any whingers start up, you can honestly say that this was democratic, transparent and utterly fair and if they have any problem with your work, the EC can sack you.
By the way, the benefits of having someone in-house doing the work must be obvious to all concerned, but someone will always have a problem with arrangements like this, so be prepared. Otherwise, go for it!