As a workaround, you could use HttpInvokers or one of the other two remoeting technologies available (aside JaxRPc): Hessian or Burlap. The latter two are quite fast, they use a very thin serialization protocol (read the reference manual part on remoting, there are some guidelines to help you choose). I am running applications in production already for quite some time using all three of the technologies and so far, it's worked quite well!
About the problem itself, could you try to publish the objects yourself and link them in using the Spring ProxyFactoryBean approach. You might want to have a look if the memory increase happens then as well... If not, than this is a Spring issue I guess...
Exporting the objects yourself is nothing more than:
Spring creates RmiInvocationWrappers to mimick the service implement Remote, so for this to work you'd have to have your interface extend Remote...
reg = LocateRegistry.getRegistry(portNo);