Not 100% sure of what you're trying to do, but you might want to look at 'process convert'. I haven't used it myself, but it allows you to call a batch process from a macro. This would allow you to get your input first and then use it as a param assuming it's the input or output directory.
If this does not meet your need, can you clarify what the 'project path' is used for? Might be another route to the same end.