Either have both of them handed to you like I normally do once I get over 100lb DB's with shoulder presses, or sometimes I "snatch" the weight up....Grab the DB's and keep them at yoru side, position yourself so you can sit right down on the bench, clean/jerk or snacth (whatever is the proper term) the weight up as you drop real quick to your butt on the bench...in actuality you only move the weight a few inches or so, cause you literally position yourself under the weight before having to lift it much.
OR
Buy those little grip hangers that you can attach to say the bar on the smith machine, and place each DB there and let them hang then just take the DB's off and start pressing.