This is a short video describing where to place a capo on a standard tuned guitar to make it playable in the same positions and notes as a ukulele.
Basically, you place a capo on the 5th fret and only play the bottom four strings. It's difficult to avoid the top two strings, but if you can manage it you will be able to practice your ukulele songs even when the only thing around is a guitar (and a capo).
The main difference in the sound will be that the top string on the guitar will be an octave lower than the ukulele. Same note and same chords, but the ukulele has one high string on the top whereas the guitar always goes down from low strings to high.