I think you're much better off using a lager strain that tolerates warmer temps than using an ale strain. WY2124 or Saflager 34/70 will get you closer than any ale strain, even pushing the low 60s for fermentation temps. The yeast character is distinctly different between an Alt, Koelsch or lager strain.
+1 I'm a big fan of 2124. Besides being clean at ale temps, it's incredibly easy to work with and forgiving. One of the best beers I ever made was a black lager fermented with 2124 at low ale temps (forgot exactly what, but I think it was around 16C) and no starter. It came out super clean and super awesome.
My last 2 beers were also with 2124. The first was a more traditional German-ish lager fermented at 11C, then I scraped the fermenter and added it to a session APA-like-thing at about 18C. I just tasted it last night and it's really clean and malty. I think if I upped the malt and mellowed the hops, I could call it a reasonable effort Octoberfest. Or something.