There really aren't that many variables in fitting a bicycle, at least for a non custom. I mean all you really have are frame size options. An additional parameter worth considering is whether you can get the handlebars up high enough, but there are options for this. This is partly the reason that many suggest getting the largest frame that you can still stand over. So it seems to me that while getting to ride the bicycle is ideal when that option isn't available you can probably still get a bicycle that fits and rides great.

First figure out the bicycles that fit your budget and other criteria that is important to you (material, color, whatever). With this short list check out all the online touring sites that you can find (here, CrazyGuy, bikeList, etc) and get peoples impression on the ride as a tourer. If you can get enough positive data points in the areas that you are interested in (stability, relaxed riding positions, what have you) then you can assume that the bicycle is a good tourer if it will fit you. You should have a pretty good idea on general bicycle fit from your current ride and you can adapt that to a tourer. Also most cycling shops can do a general fit for you and you can adjust for their biases. Most importantly you can measure your Pubic Bone Height and use that as a guideline. Check out the fitting advice from Peter White and Rivendell, much of it can be done w/o the bicycle there and then that data applied to your list of options..

This method of online research minus the fit pretty much works for anything. Any time you can get a large number of data points on the aspects that you deem important you are able to make an informed opinion. This may seem obvious, but I think it is worth stating. It has worked for me for my tent, sleeping bag, digital camera and my latest bicycle.