There are some laptop manufacturers that let you make Fn key sticky. For example, Toshiba provides this utility for some models via Toshiba Accessibility software. The users manual says:
You can use the TOSHIBA Accessibility Utility to make the Fn key
Apart from that, some Lenovo models support this function via BIOS settings. I know, for example, T60p has a setting in BIOS:
Fn Lock: Enabled / Disabled
This lets you make Fn key sticky.
I don't know if there is a global solution for that matter, but you can check your laptop's accessibility settings or BIOS settings to discover if there is one.