[boost] [Parameter] template return type

I am trying to use Boost.Parameter to construct some objects, much like make_tuple(A,B) does except with some of the arguments being optional and replaced by defaults (which may depend on the other arguments). The return type, however, must be a template class with the template arguments dependent on the arguments supplied. Is this possible? How can the return type for a Boost.Parameter frunction be specified as a template type? Thanks for your help. Cheers, Brook