I've seen home made toe jacks (online) made from bottle jacks. They don’t look overly hard to make, might be an option, although AndyA's method sounds good. Coincidentally I was in a club workshop at the weekend, and there were a pair of extremely strong trestles someone had welded up to support some girders they are working on. Could probably borrow them if they're not too high (will check how high the knee goes.
I'd prefer to lift from above but the ceiling joists/rafter ties may be in way.
The cast base only touches the ground at the corners and middle with 15mm clearance on the rest of the base, so there shouldn't be too much issue using toe jacks.