Thank you for suggesting this template Sebastian, this is exactly what I would have done. You can actually have a look at our sdk examples with WCF Plain Services that is build using these templates.
You should know that we are actually working on improving the plain services code generation trough our new and revamped DSW wizard. It will be able to create all of the needed DTO classes, assemblers and services. This will be included in the Q3 release.
Until then though I suggest having a look at the knowledge base article. I hope this is helpful.
the Telerik team