Take the two fat strings off your guitar. Put a capo on the 5th fret. Now it drives just like a ukulele!
In theory, anyway. All your fingering shapes will work, if you can train your hands not to go for those two big fat strings. Easy enough for something like the "D" shape, (which makes a "G" on a uke), but for shapes like "G" (uke"C"), or "C" (uke"F"), your fingers will stubbornly apply themselves to open air, or the wrong strings, for a while. There's no way to get around the mental drag of forcing your fingers not to do the wrong thing, except practice. It won't take long, then you can turn your attention back to your song.
Holding and strumming are also different, and you can't assume you can transfer them from the guitar. I'm surprised at how many people I've heard say that they have figured out the uke, but wonder why it still sounds like a guitarist playing a little guitar, not so much like a uke. It's because they hang it from a strap, or use a pick, or strum the way they would a guitar. What you strum with, where your strumming hits the string, where the uke is in relation to your body, and where parts of your body are in relation to the uke, are all elemental to it's sound, and quite different from how it happens on the guitar. It's very very easy and very very worthwhile to learn to hold and strum a ukulele as a ukuele, not as a tiny little guitar.
The Primary Lessons at UkeSchool.com are designed both for habituated guitarists and people who've never held a musical instrument in their life. It is much easier to learn to do this properly than it is to stop fretting those two strings that aren't there!!! So do yourself a favor - devote one hour of your entire life to discovering how to hold and strum your ukulele, rather than waste one minute trying to move your right hand skills straight from the guitar to the uke.
The biggest hurdle for a guitarist learning to play the ukulele will probably be re-naming all the shapes and patterns in your head. When the music calls for an "F", your brain will have let go of the "F" shape it knows from the guitar - and be able to transpose up a 4th - or down a 5th - so you can call up the shape your brain knows from the letter "C". It's just like learning a foreign language - you get by at first by translating everything into and out of your native tounge, and one day you surprise yourself by realizing that you don't think about it any more, you just do it.