What are you planning on doing, playing it in first position?

Oh, I see, I thought you said you couldnt play in third position.

If you will accept a bit of advice I think its good to challenge and stretch yourself, Spohr said if you dont constantly challenge yourself you will go backwards.

I would play each note as slowly and perfectly as I could before moving to the next note, third position isnt magical and its no more difficult than first, its just repetition gettin used to where you put your fingers all over again, which are slightly closer together, which is why I told you from the start train your ears because if you dont it becomes harder the higher up the neck you go  see what I mean about tapes now. If you know what the note sounds like its easier to hit it, I play all my practice pieces in third position, I hit bad notes constantly but I correct them and eventually I will get them all bang on. 

If you want to practice vibrato, without it being in a piece you cant go wrong playing two octave d major scales in first position vibrate b with your first finger, then  c sharp with your second, and d with your third, and if you are feeling adventurous e with your little finger. then the same backwards, like fiddlerman said if you want faster vibrato just cut down the width you move your finger,. just dont do the wrist thing like I said in other posts, because its wrong.