Thank you very much, Nirish, for mentioning the van. I had a look at their website http://www.pttaxiservice.com/ and they do vans to Hua Hin as well (why did I not get the idea on my own?), exactly what my friend is looking for.

So far I did not pay much attention to the recurring "Taxi to Pattaya" topics, but now that a friend has the need, which other services (websites?) are there?