Brew a lager recipe, use W-34/70 dry yeast (Wyeast 2007 works as well if you prefer liquid yeast), pitch at lager rates, and ferment at your usual ale temps. Bottle or keg as usual. If bottling, let them carbonate at room temp for 3-4 weeks (check a sample to make sure it has hit it's desired carbonation). If kegging, carbonate per your usual procedure. Then store your packaged beer under refrigeration for 2-6 weeks to "lager" in the final package.
There are many yeast strains (not just the ones I listed) that will make a beer that will pass for a "lager-style" beer even when fermented at warmer temps. And by "pass" I mean you wouldn't suspect that it's not a lager if someone handed you a cold one without telling you. Cold-conditioning after fermentation will certainly help if you can do it.