make a pot of good coffee or tea, save the beer,, and google instructables etc also check out diy counter pressure bottle fillers as they too utilise a similar beer/gas pipe within pipe solutions
corny posts will be the costly aspects, but make sence when used alongside corny kegs.
also consider adding straps to retain the spear/bung seal otherwise a lil overpressure could pop the spears..
the trick involves a large diameter to small diameter adaptor fitting and fettling the small diameter tube stop from within the fitting. this allows you to insert small diameter tube for the beer pick up
into the centre of a larger tube to seal with the keg bung and provide co2
easiest ive seen uses beerline and jg fittings 3/8" tube to feed co2 and seal with the bung, 3/16" line
for beer out fed into a modded 3/8" to 3/16" jg adaptor a 3/8" equal t to join gass in and beer out above a short 3/8" stub and long in keg 3/16" dip tube..
be prepared to screw up a few jg reduces modding to remove the internal pipe stop while retaining seals on the microline.. google a few tech drawings of the fittings etc ..
(brass compression fittings are a doddle to mod in comparison, simply drill it out.. )
slow manual turning of a 3/16" drill bit from the 3/8" opening to shave out the tube stop in a JG adaptor may work, ??
check out jb-weld or waterweld for an epoxy seal all solution if needed
good luck..