As a frequent business traveller myself, I can't imagine hauling more than I have to on a business trip. Between computer bag and clothes for the trip, another bike bag (plus the cycling gear) hardly seems worth it (unless you knew you were going to be in one place for several days). When I travel, efficiency is key. But that's me.
Like Simi, I've found elliptical trainers to be the best to provide conditioning that's
similar to cycling. I can't run or use treadmills because they are too hard on the knees. Many hotels have gyms, and most of those now have elliptical trainers (at least in my experience--I'm sure it depends on the hotel chain). As suggested, you could also get a local gym membership that allows you to use any gym in their national chain. Or, once in a city, find a local gym and get a day pass. I also wouldn't rule out the possibility of renting bikes (in some locations).
A final option might be to find a LBS in the city you are travelling to, pretend to be a buying customer, and go on a long test ride (just kidding, of course).
