Success!
I accomplished this with two LAN rules, which I forgot to move to the top, duh. One for Hulu/PC routing to WAN, another for Server routing to PIAVPN. Marked the latter one as NO_WAN_EGRESS. Created then a floating rule.
Question: PIA has a few US servers. Can I create multiple interfaces and use them for failover? E.g. PIA1 US-EAST, PIA2 US-NY, if PIA1 goes down, pfSense will try to bring up PIA2.
Action: Reject
Quick: Checked
Interface: WAN (you can also select multiple WAN interfaces or an interface group here)
Direction: out
Protocol: any
Source: any
Destination: any
Description: Reject outbound traffic marked NO_WAN_EGRESS
Advanced: You can match packet on a mark placed before on another rule: NO_WAN_EGRESS