Yes. You will need to add some custom coding for that. Not something thats supported out of the box.

I'm not sure how the Shipping Rate provider will help -- I've been giving this some thought because I have products that are shipped by vendors that only use UPS Ground. But for this to work, then the add on needs to modify the base package to only show the allowed method as a choice for shipping, and I'm not quite sure how this could be accomplished.

I am often asked how to limit the shipping methods for certain products. There are (at least) 2 ways to do it: one is possible using my Shipping Rate Rule Providers, the other would only be possible with a major rewrite of BVC5 and ultimately would be confusing.

1. Possible using Shipping Rate Rule Providers
Using my Shipping Rate Rule Providers, you split up the order into various groups: one for products that can ship by A, another for products that can ship by B, etc. Then retrieve the cost of shipping each group. Finally add the individual costs together and present the result. This is what Mitch is doing. The final cost might be called "Standard" or "Fast" or even "UPS Ground", but the calculation would be: send XYZ via UPS Ground + ABC via USPS. This is the same technique that Amazon uses (and they seem to be quite successful at it).

2. Requires rewriting a portion of BVC5
Some people want a page like this during checkout:

Or this:

Both of these would require a pretty significant rewrite of BVC5, and ultimately I think they would confuse shoppers.

A very simple non-complicated way of doing it would be this...

Assumption:
1.You only have a limited number of shipping methods (possibly less than 10).
2. A majority of your products can be shipped using any of the shipping methods, so you dont want to restrict all products to specific methods. You still could but that would require more configuration work from you.
3. A minority of your products are constrained to be shipped by a few shipping methods.

Solution:
1. Maintain a mapping of which product/SKU can be shipped by what methods (you can choose 1 or many) OR which product/SKU cannot be shipped by what methods (you can choose 1 or many). You will need to configure this obviously. If a product is not configured exclusively, that means the product can be shipped by all available methods.
2. Maintain a priority for shipping methods for:
Lets say if an order contains multiple line items and they resulted in different shipping methods, then determine the shipping method with the highest priority and show that only to the user. SO the user will not be presented a shipping method if atleast one of the products cannot be shipped by that method.
...
...
There can be n options there. Nothing is limiting us to do it. But is that what everyone wants? We could definitely customize this on a case to case basis because everybody's requirement is different. It can go as easy or as complex as required. Every merchant will have his own shipping requirement.

I have implemented this in a small way for 2 stores. One of the store doesnt want to offer First Class USPS if the weight of the line item is greater than 1 lb. That was the only restriction. So implementation/configuration was pretty simple, check for presence of at least 1 item in the order that weighs more than 1 lb. If condition evaluates to true, drop the First Class USPS shipping method. So that was a pretty simple implementation.

Hence, in order to keep things simple, and not confuse the Customer as well as the store owner, things like this should be implemented based on store requirements.