While searching for a solution, I came across these cheap, all-metal white LED bolts:
The price was right at less than $4 with free shipping. They took just over a month to show up, but I didn't mind the wait.
Installation was straight-forward. The tail light wire on the CB550K is brown, and this wire always has voltage on it. The green wire with the yellow stripe is for the brake light, and the solid green wire is ground. I just stripped back the insulation on the appropriate wires and soldered on the leads from the LED bolts. Care needs to be taken to make sure you have everything already over the wires, as once they're soldered, you won't be able to get any nuts or washers over the studs. That might be the only drawback to this style of light, but I don't think I'll need to take the license plate off for quite some time.
The other thing I did was place some foil tape on the inside of lens to block the red light from bleeding onto the license plate:
And the finished product:
