Hm, I would be careful about this. IIRC, Rick Guerin did something similar, and he ended up selling his Berkshire shares to Buffett @ $40 a piece to satisfy a margin call.
Works until BRK falls 50% as it has done 2 or 3 times.
Leverage always works....until it doesn't. Or as Buffett says regarding leverage---"if you are smart you don't need it and if you are dumb you have no business using it."