Prode includes several solvers for columns but you can access most data (input spec, results) and it shouldn't be difficult to modify something by code, the column.xls page included in distribution provides a good example of how to enter data and extract results with VBA , there was a discussion (about optimization) in the manual but the last version "http://www.prode.com/docs/pppman.pdf"doesn't mention the topic...
anyway, If you wish to investigate different configurations with different position of feed(s), number of trays etc. I suggest to create your own code instead to use a generic Solver, it requires time but there are many advantages when dealing with errors (for example Prode can't solve the column due to unfeasible specifications or similar problems...)
In my experience the Excel Solver is good for solving continuous functions (of several vars) but little more...