Using sudo virtualbox definitely works, but it's a pain in the keister if you need to launch it all the time. I've made this a little easier by creating and AppleScript through automator. This is the code:
on run {input, parameters}
do shell script "/bin/bash -s <<'EOF'
cd /Applications/VirtualBox.app/Contents/MacOS
./VirtualBox
EOF" with administrator privileges
return input
It'll prompt you for your password—or you and poke the the fingerprint reader if you have one.
Cheers!
Mark