This is what my family did once and it worked pretty well. Pound a stake in the mud about 20 yds out in the water. Tie an bike inner tube or some kind of springy material to it. Tie a line to the other end of that and then run it into your blind. Have the decoy on that line somewhere (just make a loop and attach it with a snap swivel).

When you pull on the line in the blind the decoy will move. One problem we had was that the line came out of the water way before it got to shore so we put a cinder block in the water, real close to shore, and ran the line through that. It helped.

One other suggestion is that you can tie a loop around your foot and use your leg to move the cord. That way you can minimize your movement in the blind.

Hope this helps.