That's probably what I'll try ultimately :-) There are guides on how to do it online, I just would have preferred a commercially available solution for simplicity.

In any case I'm now in a position to experiment and test the viability of the project. If it turns out well then even the cost of a hydraulic pump and ram would be well worth it (8 uses would recoup the cost!).
If anyone is interested the diagram I found is here:
http://www.free-instruction-manuals..../p47111365.pdf
That safety valve does look tempting :-)