After looking at the FSM, I figured it out (duh). The silver thing on the fuel rail is a fuel damper. From the 2004 FSM:
"The fuel damper is used only to help control fuel pressure pulsations. These pulsations are the result of the firing of the fuel injectors."
It also refers to a 'Standard procedure for fuel pressure release':
STANDARD PROCEDURE - FUEL SYSTEM PRESSURE RELEASE
Use following procedure if the fuel injector rail is, or is not equipped with a fuel pressure test port.
(1) Remove fuel fill cap.
(2) Remove fuel pump relay from Power Distribution Center (PDC). For location of relay, refer to label on underside of PDC cover.
(3) Start and run engine until it stalls.
(4) Attempt restarting engine until it will no longer run.
(5) Turn ignition key to OFF position.
CAUTION: Steps 1, 2, 3 and 4 must be performed to relieve high pressure fuel from within fuel rail. Do not attempt to use following steps to relieve this pressure as excessive fuel will be forced into a cylinder chamber.
(6) Unplug connector from any fuel injector.
(7) Attach one end of a jumper wire with alligator clips (18 gauge or smaller) to either injector terminal.
(8) Connect other end of jumper wire to positive side of battery.
(9) Connect one end of a second jumper wire to remaining injector terminal.
CAUTION: Powering an injector for more than a few seconds will permanently damage the injector.
(10) Momentarily touch other end of jumper wire to negative terminal of battery for no more than a few seconds.
(11) Place a rag or towel below fuel line quick-connect fitting at fuel rail.
(12) Disconnect quick-connect fitting at fuel rail. Refer to Quick-Connect Fittings.
(13) Return fuel pump relay to PDC.
(14) One or more Diagnostic Trouble Codes (DTC’s) may have been stored in PCM memory due to fuel pump relay removal. The DRBt scan tool must be used to erase a DTC.
Now that I think about it, I don't even know why I was worrying about fuel pressure since the check valve in my fuel pump has been bad for several months now, so it doesn't hold fuel pressure anyways.
Note to self, I should really use the FSM more instead of asking dumb questions here. It's been very helpful on the last few jobs I did.