'Do you think this will work with most recipes?'
I think it will. The thing about intentionally stronger flavors is that they tend to mask other unwanted flavors that develop over time. Precisely why brewing a light beer (say, a Helles) can be so difficult; every little flaw will come through, having no strong flavor to hide it.
'...add more hops, more speciality malts (a little more priming sugar?) '
Hops: yes (though hop aroma fades quite rapidly, making a fresh, lively hop profile unlikely to survive six months). Specialty malt: yes (the stronger, maltier flavors should serve well to cover up any age-related off-flavors). Priming sugar: probably not (unless it doesn't ferment, leaving sugary sweetness, all this will do is carbonate the beer more). It might be a good idea to just take a recipe and scale it up wholesale (add x% more of everything), remembering that higher-alcohol beers tend to age more gracefully than lower-alcohol ones.
'Any tricks for longer shelf live?(besides putting them in a fridge...)'
Avoid oxygen like the plague (this is what ends up taking down most beers in the long run), being particularly wary during transfers. Bottle-conditioning re-invigorates yeast, helping it to scavenge any dissolved oxygen present. Keep the beer out of the sun. If at all possible, find a cooler spot (18°C is warm for storing a beer for six months and every degree you can shave off will extend the shelf life, if only a little).
Other than that, you're at the mercy of the fact that every beer has a limited best-by lifespan (six months is pushing it for beers of moderate strength) and there's really only so much you can do.