I know it has taken me more than two years to come up with a work-around solution to this deficiency in Streets and Trips but I offer it nonetheless and also in full recognition of the fact that this does not seem to be a burning issue for you other S&T users nor Microsoft who does not seem to be inclined to deal with it.
The following steps convert multiple route stops to a pushpin set. One route is converted to one set but, of course, you can combine multiple sets into one map file.
1. Open the S&T map file that is populated with the stops you want to convert and export that file to GPX [Data>Export to GPX file], naming it anything you like.
2. Open that GPX file in Excel as an XML file, a prompted choice, and clicking on "Yes" when queried about the 'schema'.
3. Save that file [File>Save as] (without doing anything to it) as an XLS or XLSX file named anything you like but bearing in mind that whatever you name it will be the new pushpin set's name.
4. Revert to S&T and open a file (either a fresh file or a preferred target file) and import that XLS/XLSX file [Data>Import data wizard]. The data wizard will now take you through steps to convert that data file to a pushpin set. At this stage you need to be careful that only three columns are active and all the others are inactive. To do this, un-tick the box entitled "First row contains column headings" in the second wizard pane and then find the three columns that S&T will use for pushins: Latitude, Longitude and Name. Select from the drop-down choices in the "Data type" row the respective appropriate heading. In my experimentations, I found that Latitudes are in the F54 column (in other words quite far to the right), Longitudes are in the F55 column, and Names are in the F60 column. At this point, the "Finish" box, the middle one of five at the bottom of this wizard panel should be clickable (i.e., not grey-ed out) and you should click on it. That will produce a new pushpin set and the map will zoom to a view of those new pushpins.
5. It is probably a good idea to save this newly-created file after each pushpin set is created as I have had S&T "crash" in the process of doing the step 4 conversion once in a while.
6. Repeat as required for multiple routes.
Note that using this approach also could be the basis for combining multiple route files into a single route. A standard capability of S&T is to convert pushpins to stops, so all one need do is to do the above for multiple sets and then select those sets for conversion to stops [Add pushpins as stops] and calculate a new route.