Running a vang back can be as easy as taking the cleat off the bottom block, and running the line back through a clutch or a 150. This assumes of course you have one to spare, along with an open turning block. If not it becomes much more complex.
The real question is where is the person working that will be playing it, and in what conditions? Often its best where it is, even on big boats. Depends.
You can double the purchase by simply attaching a length of dyneema to the same attached point the vang uses, and secure the other end to the top block of the vang which has been detached form the boom. Run the dyneema for a good sized block attached to the boom at the point. Size the line so you have good range of motion. Easy 2x advantage. 10 minute mod.