Is there any way to match Vth of 2 mosfets with different aspect ratio?
Look carefully, M1 and M2 are simply made up of different number of the SAME transistor, i.e (W/L)N. M1 contains 1 unit and M2 contains K units. This is how you achieve the best matching. 

Trying to match Vth of different sized transistors is a hopeless venture even on the same chip! Heck, Vth matching of same sized transistors in different locations is hard enough and can be very layout dependent. Different sized devices will always give relatively large systematic mismatch error.

The best way to improve matching is by using area. Mismatch error for MOSFET's has been famously shown to be:

1) proportional to thickness of oxide - So thin oxide devices achieve best matching!

2) Inversely proportional to sqrt(WL) - Large area means good matching