exclude a few products from one shipping service

Goodmorning all.

I have a question. People who order something at my webstore can choose between two- shipping services. One is cheap and one is a little bit more expensive but much more reliable. Because some products are too large for the cheap service I want to exclude them from it.
I want that if somebody is ordering one of these products that only the more expensive service appears.
Is this possible?

What methods are you using now?
What are they based upon?
Are these heavy items all in one category?

I am using the zones.php for the normal shipping service and the zones2.php for the cheap shipping service. The items are not in one categoy, but I can add them in one category if that would be easier

What if someone orders two items, one that works for the cheap shipping and the other does not?

I use CEON's advanced shipping mod, but it may be overkill for your situation.

Something like this might be customized to look for 'Shipping_Method = 1) and enable/disable the requisite shipping module.

http://www.zen-cart.com/showthread.php?120145-Can-I-restrict-certain-payment-methods-for-certain-products