Game night at my FLGS tonight, I made an attack with Garven and rolled 2 hits and 2 blanks (R1 shot) - I declared that I was converting zero focus into zero hits to use Garven's ability to pass the focus.

Nothing was said but I got a look from one of the spectators (who happens to be one of the better players in the group) that I'd made a questionable rule call - but I'm about as certain as I can be that this is OK.

Was I right?

Perfectly legal, and addressed specifically with Garven in the FAQ.

That is specifically called out as legal in the FAQ.

Yes Garven or anybody can use a focus token even if there are no eyeballs. Keyan can do the same with a stress token.

I will even go further to say that your move was not only legal but absolutely kosher in every way. I can't imagine anyone taking exception to your move. Used as intended and in no way cheesy or exploitative.