The "remote" part of this Instructable stems from the fact that the trigger is away from the actual switch, so that you needn't sit within reach of the ethernet cable it controls.
The "controller-embedded" part uses the battery shell from a wireless Xbox 360 controller, so take note that you'll want to have a Play & Charge kit to use the controller. The rechargable battery in the kit replaces the battery shell that comes with the controllers, so most will have no use for it, and the cable will supply power to the controller whilst using the lag switch.
You can also adapt this Instructable for use without a controller, simply by placing the trigger in another enclosure of some kind. I've thought of placing it in a box by my foot, so I can just "stomp" on it when I want some lag.
Step 1: Parts and Tools
Wire cutters & strippers
X-acto knife/Stanley knife
Ethernet cable (the length is up to you, I used a short one as the distance between my router and Xbox is tiny.)
Enclosure/project box (again, size is up to you, but smaller is better in this case.)
Spare Xbox 360 controller battery shell (it won't ever hold batteries again, make sure you aren't using it.)
Generic hook-up wire
Shielded wire (we'll be using the shield as another wire, feel free to substitute a different type of wire.)
Two watch-battery holders (CR-2032, CR-2025 or CR-2016 recommended.)
Two watch-batteries to suit the holders
A normally-open push button (I used a button that had both N.O. and N.C. but it's not necessary.)
A SPDT (single-pole, double-throw) 6 volt relay
All up, this should cost you under $15.