Run an overflow box, unless your tank is already drilled, down into the 29 as if it was a sump. there are a lot of posts about doing this, pretty basic.
Add a pump with a rating that will work well with the overflow of your choice.
Instead of building a traditional sump, using baffles and drip plates and bio balls or what not, just set it up from there as a refugium. get a small powerhead, like a rio 90 or something to give you a gentle current in it. place the return pump either directly into the 29 gallon tank, or make some sort of divider with acrylic if you want it in a seprate compartment, and run that back up to your main tank, using either a plain pvc line to flow back in, or a make shift spray bar if you like.
Pumps for that size tank can be found for about 50 dollars, about 10 bucks for plumbing, and then whatever you spend on an overflow, either one from the fellow here who makes them (i think like 50 or 60 bucks) or one from a manufacturer like CPR for about 100 bucks... so 110-170 or so in construction costs there abouts?
