As a supplement to JeremiahD's suggestion, I would also try applying heat. There is some debate as to whether this car is fitted with nuts or bolts - if it's a nut, heat could be applied to the socket/extension bar while a turning force is applied(encourages the socket to establish thermal conductive contact with the nut) thus keeping the flame away from the alloy. Bear in mind that radiated heat may still cause damage to the alloy
If it's a bolt, heat would be best applied to the back of the bolt rather than the head of it. For this you'd need to get under the car and have a look to see whether any part of the bolt is visible, or whether anything can be removed or have a hole drilled to grant access to the threaded end of the bolt
The suggestion to try turning the bolt the other way (in the comment about it possibly being a reverse thread) may also bear some fruit- I've occasionally managed to free stuck bolts by getting a fraction of movement clockwise before undoing counterclockwise
Failing these, boning up in your metal drilling technique and using a high quality drill bit, you may find it faster to drill a succession of small holes in the head with the aim of weakening the part where the head joins the shaft, shearing the head off then using heat and grips to extract the remaining stud
In terms of using your new 750mm breaker bar more effectively:
1) Select a socket that is a hexagon shape with what looks like rounded out corners (as if 6 holes were drilled then the hexagon were cut between them) like this:
These are much less likely to round a nut than straight hexagon or (worse) 12 pointed sockets (a hexagon overlaid on another hexagon). The reason for this is the rounded corners apply force not to the points of the hexagon on the bolt, but a few mm away from the point, where the bolt head is stronger. A straight socket applies force directly on the pointy bits of the bolt head, encouraging them to round off
2) ensure that the socket is pushed as far onto the bolt head as possible, especially if it has already started to deform. Use a hammer to knock it on if necessary
3) take your hydraulic jack and jack it up til it is supporting the head of the breaker bar (where the bar turns 90 degrees). Broker bars and sockets must extend away from the wheel some way before they turn 90 degrees to become a lever. If the distance they run before they turn is great (like 6 inches) then the downward force you apply to the bar will attempt to bend the bar downwards off the nut. By supporting the bar where it turns 90 degrees you stop this from happening and convert all the force you apply into a rotational one. If the breaker bar were a T shape and you pulled one side up while you pushed the other side down, it would also relieve this problem. Most breaker bars are poorly designed and extend too far away from the wheel, encouraging your downward force to bend the bar off the nut
4) make sure the breaker bar is as horizontal as possible; the more vertical it is the less torque your downward force is applying, as the turning force applied by a vertical weight is a factor of the horizontal distance between the bolt head and the force
