Random weighted loop without the same stimuli touching

Hello!

In my experiment, I am supposed to repeat different stimuli for a different amount of time (for example, stimulus 1 will be shown 5 times, stimulus 2 10 times, etc.). In order to achieve this, I've manually weighted them (I have each of the repetitions as a single stimulus). Now in my table I have s1 s1 s1 s1 s1 s2 s2 s2 s2 s2 s2 s2 s2 s2 s2 s2 s2 (vertically, of course). Now, I need to set up a way to never show the same stimulus to a subjects twice in a row - so my order of appearance of stimuli would need to be s1 s2 s1 s2 etc. It's not only 2 stimuli, of course, just writing it as that for simplicity's sake.
So, in short - I need to have my stimuli repeated variable times without appearing twice in a row and being completely random (random for all subjects).

Thank you in advance!
Slobodan