I used heatgun method along with a bunch of others during a group install. It does take longer but with careful aiming you won't melt the plastic.
The entire install time (remove bumper, headlights, heatgun, install dde's and wait for it to dry in place, sealing headlights, reinstall headlights, bumper, wiring) took a day to complete. Maybe because we had to share two heat guns and two sets of tools for five sets of dde's to install but yeah..
Using the heat gun to open the headlights probably takes about 10-20 minutes each headlight, have a friend help you out as you heatgun, get them to use a tool to wedge into the housing to break the seal for you.