How to wire a three phase machine to a single phase plug?
You can't just fix this with wiring.

You either need to get 3 phase supplied to your location and wired to the device, or you need a phase converter, such as what these guys sell:

http://www.northamericaphaseconverters.com

A possible alternative might be to use a VFD, such as this one:

http://www.automationdirect.com/adc/Shopping/Catalog/Drives/GS2_%28115_-z-230-z-460-z-_575_VAC_V-z-Hz_Control%29/GS2_Drive_Units_%28115_-z-230-z-460-z-_575_VAC%29/GS2-11P0

In either case, I would seek advice from the device manufacture's tech lines to confirm it's suitable for your application. These devices are generally expected to be connected to a motor, and you have a heater - that is an electrically significant difference.

Also note that I doubt the 3 phase is just powering the boiler. I don't know coffee, really, but I thought high-end espresso machines were pump driven - the pump will be 3 phase too I suspect.