I have not tried the css3-mediaqueries.js! Maybe you give respond.js a try. This actually works for IE 6-8 which natively do not support Media Queries (see Can I use ...).
Anyway, why would you still support IE 7 nowadays?
Each system still running an IE 7 may be updated to IE 8. And also the fallback for modern CSS3 layout features like Flexbox is much easier cause of IE 8 support for 'display: table-xy' (which is not supported by IE 7).
Personally I do not use any Shims/ Polyfills for the basic layout because in my opinion it is counterproductive to make the CSS layout depending on Javascript support.
