Shipping different suppliers doesn't add up in Cart

[Justmetrying]

Hi, I'm a dropshipper. I have a supplier who sells based on volume, so if you spend $10 to $50, shipping is $5... if you spend $100, shipping is $30, etc..  I have another supplier who sells flat rate.  For one bed it's $54.  So here are my problems:

1) If a customer buys 2 beds, shipping still shows as $54 instead of doubling the shipping cost to $108

2) If a customer buys 1 bed (shipping $54), and two items at $50 from the other supplier, the volume rate of that other supplier kicks in and some exorbitant amounts show, Like $80 shipping for $104 order.... 

Is there a way to separate the two and have the actual amounts added correctly in the cart?  i.e. for the example above it would be $54 for the bed and $5 shipping and not the $80 which kicked in depending on the volume-based amount of the cart bought from the volume-based supplier.  

Thanks