Yeah, I know the technique. Had a bug on 25 and everything. I found myself still behind the plane very suddenly because the conversation around which runway to be on with the local controller ate up my margin. Still my fault for not anticipating it.
Basically, I had oriented myself to a left 45 entry to 30. That naturally put me head on to 25 departure. I should have realized that would happen. It was a problem even with getting a 30 clearance. Not sure what happens normally, and I should researched that better. I was getting pretty close when I was switched to 25L and it took me 10-20 seconds to figure out what I was going to do. What I did do is turn right to make for a very non-standard left crosswind entry to the 25L pattern. Ugly. Still not really sure how I should have handled it when I was that close already.
EDIT: The standard answer of overfly and teardrop doesn't work because of the very active 30 and usable, but dormant 25R. I'd end up in the 30 pattern either way. The right thing to do, if I really wanted 25L, would have been to swing out much earlier, before I was inside the Delta, so I could have done a standard left 45 entry. If I were thinking ahead, that's what I would have done, but given that I'd already screwed it up...not sure how to have corrected it.