It is not possible unfortunately. There is free episode 2.0 on my website to test the game. It is also one-time-purchase, so I believe it is not that expensive overall.
With all due respect:
(a) to create a game you have to spend a lot of money on it, so ultimately the developer also wants to make money, this is probably not a discovery of America, without funding, there is no way to pay graphic designers, programmers, writers, translators, etc.
(b) according to Steam's terms and conditions, if I offer, at some point, a discount/promotion then the same promotion must also be on Steam - so if I make the game available for free after a week after the update, I will have to do the same on Steam, and then see point (a)