I've attempted most other ways with failure, but this is how I do mine successfully every time within a minute.
Use a 6 inch G clamp and a small piece of timber(the timber in the picture is long just so it could be seen for photo). Wind up till bead breaks then rip tyre off as per norm.
No mods to rims and very quick and the clamp is small enough to take on trips.
There is a thread on this but I couldn't find it again.
Happy bead breaking