Improve Customizability of Expression Language for Webflow

If I wanted to register a new function to be available within a webflow expression, e.g.:

<on-entry>
<evaluate expression="#beginBusinessProcess('registerCard')"/>
</on-entry>

I think I need to add the method 'beginBusinessProcess' to the standard evaluation context that Webflow is using. In order to do this, I have to wire in a completely new 'SpringELExpressionParser' implementation to replace 'WebFlowSpringELExpressionParser', as well as completely re-implement 'SpringELExpression' so that I can provide a new evaluation context. My reimplementation is brittle since updates to webflow's expression parser will be lost (particularly if new property accessors are added in the future).

It would be useful if there were a protected hook point that I could implement, such as 'handleEvaluationContext', whereby I could tinker with it before it's used.