The main bottleneck in docked mode is the thermals, which is why the Switch's Tegra chip is severely underclocked even in that mode.
So what you would need, ideally, is beefier cooling in the Switch 2 (but do consider you have to balance the size and weight of the cooler and heatsink against kid hands and weak-ass kid's arms).
Alternatively you could include the cooling on the dock itself though external solutions like this often do not work well (most being effectively scams for clueless laptop and also X360 owners in the past).