This question doesn't really belong in this thread, and should really be in the Shipping & Payment Modules but, if I understand you correctly, you want to have free shipping on this when it's purchased with anything else (use the Cross Sell mod from the downloads for "suggesting" it) and shipping by quantity if bought alone. Are the shipping charges on this item different to your other products, and are you intending just to tell the customer "The total shipping is $xx" ?
If that is the case, and the answer to both questions is yes, then I think the only way to achieve that is by coding.
The logic is straightforward - examine the cart; if a product belongs to a certain group (which you could identify by adding a single letter to the beginning of the item model no) use a specific shipping module and then total up the individual shipping costs for display to the customer as a single shipping amount.
The coding is totally beyond my ability!
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