The idea is to instantiate sub-processes based upon conditional expression. This would give immense flexibility while modelling the process.
You could put an expression in "calledElement" attribute which is evaluated at runtime and the resultant string is taken as the sub-process name.
After some look into the engine I have found that the engine accepts "string" as the parameter for sub-process name, directly from the xml's attribute.
If somehow it was allowed to have an expression evaluated rather than just taking in a string it would solve the problem.