I've never ran CO2 into a canister and probably never will. So with the "never say never" thing in mind. Heres what I'd try to do...
This is intended to hide it, as well as let you see your lil bubbles going in.
Reference this>
http://www.drsfostersmith.com/product/prod_display.cfm?c=3578+3669+3690&pcatid=3690
In the top pic. Get some airline suction cups. I got a box(6-8 pcs) of them from petsmart a while back for my co2. I found 2 that the clip actually stayed in the suction cup easily. The others were so loose they'd just fall out if you so much as turnt it sideways. Nothing that silicone wouldn't fix. But I got the two I needed at the time, so I didn't need to fix any.
The lower pic. See the L bows?
You might be able to find a 1 or two pack somewhere. Opposed to this $5 thing, to use 1 of. If you haven't made the trip to Ace hardware yet, look there for 1. A black 1 would be good.
Now with that stuff. Hide the airline behind the intake tube of your canister. Using the suction cups against the glass. Hopefully there's enough room? If not, pffft... cancel this idea.
If were moving on...
(Have the L bow in place, before sticking the line in... details, desmails)
Now have the L bow facing right at the bottom of the intake. Ta dahhh. Bubbles sucked into the canister.
The airline isn't noticeable by your neighbors looking in your window from their window. Gauuuud I hate hoses, tubes and wires.
But you can sneak a peak from the side and see your bubbles bubbleing. And know its working.
Most likely what you'll see, is. In the airline. Water going back up into it about an inch, then keep getting pushed back out by the co2. Over n over. Once you see the water, not get pushed back out. You should have changed the co2 bottle 2 days ago.