As barls said. When you remove the empty bottle it lets go of any spare gas so you can't do a second with same bulb.
BUT have tried the following with success.
1.
Inside the tapking there is a small white regulator, remove it.
High pressure side is flush against bottle lid a small 6mm OD tube does a U-turn which takes low pressure side into bottle.
Only takes 1 screw to remove but you need to remove 6 to access it. (All Phillips heads)
2.
Now push about 1cm of that tube into a 6mm ID tube and put a clip around it. (Clip not shown in pic)
Drill a hole 8mm hole in tap keg at about '11 oclock' and feed the 6mm ID tube out of there. Connect that 6mm ID line direct to your CO2 regulator and gas.
3.
Reassemble and use the tapking exactly as before.
A: It won't pierce the bulbs now and you can reuse those lids in an unmodified tapking with homebrew or megaswill.
B: Pierced (used) lids can be reused with homebrew or megaswill in the modified tapking, don't undo tri-screws on lid and never buy bulbs again.
I've just done this with a full size regulator and gas bottle but have ordered one of these today so regulator & gas can both reside in fridge. The 16g bulbs are available at brew & bike stores easily.
http://www.ebay.com.au/itm/281150299353?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649
I reckon 1x 16g bulb should do 3x 3.2L tapking bottles but haven't tested that yet.
Still working out the optimum pressure, could test the old regulator but would waste a bulb and need to reinstall everything. Let me know if anyone works it out but my guess is 15psi??
I can't work out how to make use of the removed regulator but I bet someone else does.
I've got 2 tapkings in kitchen fridge now, one takes bulbs, one takes gas. $46 total cost for 2-tap keg setup not bad. That assumes you have CO2 reg which I did.