We had a similar half wall in our kitchen. One thing we did was to take a few of the 2x4's that's part of the wall and take them through the subfloor to the trusses below. Had to use some 2x6 between 2 trusses to get it all to line up. The win here is that the wall is a lot more stable. If nothing else, I'd try to get the dead end of the wall since this is something that will get run into. That way, both ends of you're 90 degree mini wall are stout attachment points.
At a minimum think about bolting the wall to the sub floor in 2 or three spots instead of just nailing it. Put a 2x6 on the other side making a "subfloor sandwich" so it not relying solely on the strength of the aventech subfloor. If the wall will have an eat in area extending out from it, this is even more important. Without firm attachment, you are relying on your cabinets to hold the wall in place and keep it from flexing. This is yet another perfect homeowner job. The framer does what they do, you come in later and beef it up a bit.
Finally, if there is any way you can talk the framer into putting a blob of glue (like the Gorilla Glue ?) on the vertical 2x4's, between the glue and then you bolt through you'll be good to go. If you make sure the glues on site, should not be a big extra for the framer to do. Seems like extra charges _really_ get extra if it's something the tradesman does not normally do...
Pete