You'd be better off using a rattle-can and masking tape. To get a feathered edge with a spray can, leave the edge off the surface by folding one edge of the tape over (about an eighth-inch works)... If it's a "mottled" effect you're after, then take a round brush, cut the bristles back to about an eighth-inch in length, and use a stabbing/stippling motion to apply the paint.
Dip the brush into the paint left on the inside of the LID and then stab a piece of paper with it until it's similar to the amount used fir dry-brushing...
You can also use that technique to go th length of the color demarcation line... It won't look sprayed, but it's as close as you're gonna get without spraying...