You could do it through xnodes and VI scripting, however it wouldn't be trivial to implement, especially if you don't have experience with either.. Why do you want this functionality? If the inputs will be the same type, why not just make the input an array?
Practical Answer: You would be very much better off by just accepting an array input.
Technically Correct Answer: Yes but it is not supported and poorly documented
I know that an array could be a good solution but I don't know the number of the inputs a priori.
Again, what are you planning on doing with those clusters in your vi? If you have 3 input clusters, what would the code do? What about 10?
In every input cluster I have a density spectrum, two number which define a band and a number which defines a threshold. In output I want a boolean signal which tell me if the threshold for every spectrum in his defined band is passed.