I know exactly the situation you are describing & getting sandwiched. Depending on what the intersection looks like, you might find it best to hang out at the very left edge of the turn lane to allow cars to get through, but a couple seconds before the light changes, if nobody is moving behind you, move forward and right to block the turn lane. If anyone gets mad at you for this, they are an idiot. This is of course assuming there will be enough space at the other side to continue riding without being pushed into a gutter.