Is it possible to define constant declaratavly?

I have a Web Dynpto application calling to some rfc enabled function. This function has a lot of table and import parameters and most of them should be assigned to constant values and not to be modified. For now I have a function in component controller called assignConstants which is called from wdDoInit function but is there any way to define this constant and bind them declarative, without coding?

P.S. It would be also nice to have something like default values for all context nodes.