I believe it's harder to do for small companies due to legal/tax reasons (something about less than 32 hours complicates things a lot although I don't know the details why).
The "simple" solution is to be good enough that you have the bargaining leverage to propose it and make it an ultimatum. Other ideas:
* Grind in a project for some years and become indispensable and then propose it.
* Propose it as an experiment for 6 months.
* Create an "excuse" of why you need the extra time such as pursuing an M.S./PhD.