It is somewhat troublesome. From what I can tell, the JSON1 extension is not enabled by default in PDO Sqlite - and I have not found a way to enable it at runtime when using PDO.
I believe the only way to get this is to compile your own PHP/PDO with json1 enabled, but I have not done so - I simply use a different query when driver is sqlite - this is suboptimal for testing, but it gets the (rest of the) job done