Chris honestly my way will be your best bet id not advise someone in this feild if I had the slightest inclination that it would fook your car !!!
You have less than 2 gallon in the tank fill it up and it will be fine mate the time you start having problems with pumps etc is when you fill the tank with petrol and drive it till it stops diesel is oil based as you well know this aids in lubrication of the bearings and internals in the pump petrol washes the lubrication away but such a small amount will not harm it ! .

Regards Doug .