Can an ab initio PPL be trained for a JAR PPL on a complex, retractable single ?
That is no problem at all, you can even get your PPL with a dual.
Insurance would be a problem - that's the first thing I would check because the person has to go solo at some stage.
In the usa you don't NEED an insurance, i don't know exactly for European regulations, i always have learned to check the aircraft papers for insurance document, but it could be that insurance is not needed to take off.