You can use a simple trick by passing an extra variable in dictionary when creating record using xmlrpc, and in override create/write method check it in context as.

In php,

> $context = array(
>             'from_xmlrpc' => new xmlrpcval('from_xmlrpc', "string")
>         ); .... $msg->addParam(new xmlrpcval($context, "struct"));

In python,

> def
> write(self,cr,uid,ids,vals,context=None):
>     if context is None:   context = {}
>     if context.has_key('from_xmlrpc'):
>         do-nothing

Hope it will solved your problem.