If you do Linderhof on the way back to Munich, the best way to get to it from Füssen is probably through Reutte in Austria. After Llinderhof, visit nearby Oberammergau.
However, my suggestion would be to spend more time in Füssen and not to have time left over. There is more to see in Füssen than just Neuschwanstein. The other castle there, Hohenschwangau, is also interesting. Although also not that old, it was a real home, where Ludwig grew up, longingly looking at the Schwanstein, dreaming of building his own castle there. Some people find it more interesting than Neuschwanstein. In addition to the castles, there is the Museum of the Bavarian Kings. If you have more time, walk around the pedestrian streets in the town of Füssen itself. Some people like the alpine slide (Sommerrodelbahn) at Tegelberg, just east of the castles, although there are other slides in Germany - it's nothing unique to Füssen.
If you don't want to stay in Füssen and want to see some attractive scenery, drive to Garmisch-Partenkirchen and take the Alpenstrasse back towards Munich through Krün, Walchensee, Kochelsee, and Bad Tölz.