I do not know if I have correctly understand your question. Thus I am going to give you my two possible solutions
1)In Common Components there is a block named Delay: Insert in into your design and double click it. Its menu that opens gives you an option about Equation Editor. A new menu opens and tells you to insert the function, in your case the sin function. If you do not how to insert it, use the Simulator Functions Control under it. Furthermore you can do a search in the Search examples using delay and you will find quite a few examples
2)I guess that you probably want to insert some kind of fading in your model. If this is the case, again search with “fading” and there you will lots of examples.
I hope that I have helped you.