The 70Hz have nothing to do with VGA per se.
VGA just happened to output 480 line modes at 60Hz and 400 line modes at 70Hz, because the monitors could handle 70Hz at that reduced line count.
In a Laptop with 60Hz TFT panel, it makes much more sense to change the VGA register tables in the option ROM to always yield 60Hz.
Any VGA card can do that via ROM modification or TSR.
If a piece of software sets the VGA registers directly, you can either intercept that in protected mode or periodically check and patch the registers in real mode.

Typically, laptop graphics chips do not need modified VGA register tables in an option ROM, but they have a set of hidden additional registers to set up LCD timings, and in LCD mode, a part of the standard VGA registers (like horizontal and vertical total) is ignored, and the fixed LCD timing is used instead. I would assume that the laptop will run mode 0Dh at 70Hz in "external monitor only" mode.

"External monitor only mode" I have found to be rather unreliable in laptops. It's supposed to make the integrated graphics chip behave like a normal video card and output the actual mode, of course, but in practice I've found it still outputs a fixed resolution with scaling even when the built-in LCD is disabled.