public class MyModelProposalProvider extends AbstractFinancialProposalProvider

        // I could filter the cross-referencings that I don't like
	public void completeProductionReturnType1_FeatureName1(EObject model, Assignment assignment, ContentAssistContext context, ICompletionProposalAcceptor acceptor) {
                		Predicate<IEObjectDescription> booleanFilter = new Predicate<IEObjectDescription>()
		{
			public boolean apply(IEObjectDescription ieod)
			{
				// Return true/false basing on your liking here
                        }
		};

		lookupCrossReference(((CrossReference)assignment.getTerminal()), context, acceptor, booleanFilter);
	}

        // But I cannot do anything to the completeRuleCall()
        public void completeProductionReturnType2_FeatureName2(EObject model, Assignment assignment, ContentAssistContext context, ICompletionProposalAcceptor acceptor) {
		completeRuleCall(((RuleCall)assignment.getTerminal()), context, acceptor);
	}
}