just a thought (and possibly a curveball): would it be worth considering addressing this requirement by adding a "expression-source" attribute for the uri-variables, and referencing an instance of: org.springframework.integration.expression.ExpressionSource

The only current impl is ReloadableResourceBundleExpressionSource (which is nice if those expressions need to be updated at runtime), but we could also add a simple MapExpressionSource that takes a Map via its constructor.