Not sure if you mind sharing your setup and especially your existing tripod.
If to guess your setup, but the usual suspect lenses would be something along the line of 16-35, 24-70 and sometimes 70-200. Which I have trouble imagine that ur tripod is unable to take the weight when vertically positioned. (70-200 have it's tripod collar so I don't think this will result in the instability. )
And if it's like the above I've listed, the "lightest" additional thing to carry around would be an L plate. Shouldn't be more than 100g....
Oh, like DD123 said.. Forget about the gear heads.... each weighs at least 1kg... and not forgetting that it takes alot of time to tilt and turn the directions. Usually this is only used when precision is required in architectural shoots.