You have to have the size to get any good amount of sweep, we could debate the usefullness of extensions all night, in my opinion they are worthless for size...great for definintion. Once you have the size then you can polish it all off with the extensions.
Rear squats naturally will build size but I have found that I respond very well with frontal squats...(barbell on chest). ALso once in a blue moon I will squat down onto a bench while keeping my feet and kness together...like sitting down.
BPP