I can't offer more than speculation: achieving rail pressure is usually the task of a positive displacement pump, similar to a cam offset roller or gear pump contrasted with the centrifugal pumps used as fuel transfers or window washers. I'd guess you might easily bypass a stationary centrifugal pump, but perhaps not one with positive displacement design. If you pull the check valve from an inline main pump, you can blow through it, but it is very restrictive compared to a transfer pump. A Regina pump may allow enough past it to keep an in-line fed, I don't know. Worthy of experiment if safely hacking an external pump is really less work than replacing the one inside.