Sorry no one has responded yet but what type of cluster words are we talking about, could you give any examples because they can range from really smooth to immediate blocking for me. For example I can't say "Chronicle" without stuttering the "Keh" sound so I end up speaking like "k-k-k-k-k-kronicle!" But for other consonants I have no problem, like I can "Please" and "Dragin" no problem. What I do to circumvent the stutter is that I just say the first part of the word slowly, so taking chronicle as an example. I would say: "Keh - ro - nickle" and when I feel like stuttering on Ch I usually do a throwaway vowel like a silent "eh" sound so that would be "eh - Keh - ro - nickle". The eh is mostly inaudible for listeners but loud enough so that I can say the K vowel no problem. But everyone has different difficult words to say, so I can't really give universal advise on cluster words. That being said I hope this helps even if it's just a little bit.