This website (linked below) has the ability to convert a Google map route to GPX. So you can make a route in google maps, add stops, adjust the route and so forth, then convert it over.
It's not quick, and takes some playing with the setting and formats to get everything just right, but it technically could do what you are wanting.
http://www.gpsvisualizer.com/
Unfortunately this is not a good solution on the fly, works best from a computer I'm sure. Technically might work from a tablet browser, but the experience sounds frustrating at best. For planning ahead of time though it could work.