Just because I'm curious, why do you wanna cut out mining addresses?
A interest for everyone with a "no transactions since"-limit on the address just above a certain threshold isn't a really bad idea. The only problem with that from my point of view are the "little" miners. Because every time they can't add their mined coins to their main address because of the "no transaction since"-limit they are loosing the interest for it.
If you make it just a interest giveaway for all above a certain threshold why is there then a need for the "no transaction since"-limit? This limit would be only needed if you make the giveaway to a limited number of addresses in a certain BTX range.