There is a fairly quick way to do it - open the file with MapSource, use the pointer tool to draw a rectangle around the area containing the waypoints you want, select COPY from the edit menu, then open a new (blank) MapSource file, select PASTE from the edit menu, and drop the selected waypoints into the new file. If you are interested in covering a route, rather than a specific city, you might have to draw a long, thin elongated rectangle along a few places that overlap your planned route, and repeat the copy/paste exercise a few times - using the same source and target MapSource files.
Now save the new file and upload it to your GPSR. You will get a '10 mile square' selection, rather than a 10 mile radius selection, but other than that, you'll get what you want done, quickly and easily.
There is another way to get the job done dynamically - if you are using a fairly recent GPSR (26xx or newer), and you have the latest system software in it, try using the FIND feature of the GPSR with the 'NEAR ROUTE' search criteria active. This will return all the hotels that meet your search string specification (e.g. 'Ibis' or 'Formula') from your present position to the end of your route, listed in order of increasing distance from you. This is what I do when I am touring - I like this feature, because I can then make my own last minute judgement about whether to take the one that is 20 miles down the road, or to press on and ride to the one that is 40 or 60 miles down the road. The hotel companies are especially vigilant about making sure that Navteq has all their properties in the database, so you don't have to worry about missing any.
Michael