I use a small wire (22 or 30 AWG) that runs up the side to the top battery with a loop to go around the positive "button", that way it doesn't interfere with the contact to the switch. One also must be careful to run the wire thru the spring higher up in the coils so it isn't crushed when tightening the tail cap, I use a little shrink tubing to protect it at that point.
Btw, use both batteries (for a 2D). If you only use one the flasher will eventually lower that batteries voltage and when you turn on the torch the stroger battery will "equalize" into the weaker one. This will result in a dimmer light when you turn the torch on after it's been sitting a month or so. If you use both to power the flasher they will drain equaly at a very slow rate.
I've been meaning to improve on this for years because it makes changing the batteries a little more involved, but it works well enough as it is. (It also works very well for charge in place units like the MagCharger.)
The LM3909 is an old but very versatile IC. It can be used for all kind of ocsillator, alarm and strobe applications.
Do not use the external resistor on the IC, it's not needed. Use the internal and just add the capacitor. I use 100mf, 10v caps. I've also used 200, 10v). (I like the thing real bright.)
Parts count of three: IC, cap, LED. I've used both T1 and T3 leds, the smaller T1 rated at 2 ma. The T3 2000 mcd red one at Radio Shack works OK also but I have some really bright T1s from Hewlett Packard.
The led can extend from the tailcap or be flush. I also have little "frensel" lens that go over them, but not really needed. I've screwed around with about a dozen variations of this thing over the years, some pretty strange.
No doubt there is a better way to do this as it's an old design (I dunno how Eveready does it), but it's work well for me for a long time so I stick with it. I'm an EE but I quit the biz many years ago and don't keep up with it much these days. I'd post some photos but I just can't get it to work in spite of trying many times. (any advice?)
If you need more info, email me.