There are several ways that you could go. One would be to check with a custom car parts retailer for 12 volt actuators which are used for opening doors and trunks, this could be operated with a 12 volt power converter such as a charger. The other and more costly way would be to contact your local Hydraulics repair shop and purchase either Bosch or Atos 110/115 volt solenoids which could be actuated by servo operated micro switches, many of these are available with internal processors that control lateral movement, ie, distance/speed/force. A light spring installed on the door hinge would help if it didn't place too much force against the pin which operated the locking mechanism, the bad part about all of these is that the lateral movement is probably less than 1 inch. If you design something which uses something like the cylinders used in the lift hatches on Mini Vans it would give you more movement but it also adds another factor to the equation.