I found by using this product (mixing mate) on a gallon size can of primer to mix and easily pour just a little or lot has saved me a ton of time and mess. Basically you just turn the handle for a bit , pour the measured amount and put back on the shelf. I am using it with the Sherwin Williams P60G2 primer but you could use it on any quart/gallon can.
http://www.rockler.com/mixing-mate-paint-lid-gallon-size-stir-pour-and-store#product-tabs
http://www.rockler.com/mixing-mate-paint-lid-gallon-size-stir-pour-and-store#product-tabs