I do remember considering it back in the 70's but can't remember if I tried it. In the end I had to replace the engine so it came out anyway. I think that it can't be done as the strainer and pick up pipe get in the way even though the engine is jacked up.
It might be easier to support the engine and drop the cross member to gain clearance. If you consider this route remember to be very careful mot to bend the steering column.
If it is only a pinhole in the sump it can be brazed in-situ. Just drain the oil first and remove the oil filler cap.
Many years ago a work colleague had an Imp, he punctured the sump a few days before going on a Continental touring holiday. A quick run to a welder and a spot of braze fixed it......or so he thought.
At morning tea break while the car was parked in the staff car park, just hours before departure that Friday evening, one of the pranksters in work who bore a grudge decided to wipe some oil on the newly brazed part of the sump, spill some on the wet ground below the engine and drip a trail from the car park gate.
Lunch time saw some frantic phone calls and trips to the Hillman dealers and local car breakers to track down a replacement sump and gaskets, then an afternoon spent below the Imp swapping over the sump with a couple of us concerned mates in attendance while the prankster sat looking out the window....
Needless to say the owner was less than pleased when he returned 3 weeks later to be told it was all a dirty trick.