Turbo, SMD LED's might be of interest to you. Cellphones and laptops use them for keypad lighting and status lights quite often with fiber optics. My eee pc has the LED's on the motherboard and a small clear acrylic piece that is flat on the bottom and rounded ends, which look and light as if they were the LED's themselves. The ends light up but the tube doesn't really, it just passes the light through, so there is something to consider there. Also, electronics in the tank is rather a bad idea as it doesn't need to be there and could/would contaminate the juice. And drilling another hole is not something I'd want to do myself, not through SS.
I carry mine all the time now in my front pants pocket, even the 18650 setup. Sag is sure, but I've been wearing jeans most always lately as it is so wintery. Not having a driptip helps that there is nothing to catch in pocket too. Dan said he even carries his in a shirt pocket, that's even too hardcore for me
Oh and the switch and a winter glove works ok, if I hold my finger thumb over the switch the whole time. Finding the switch with a glove is not possible.