Make a views of data entered in composed fields
Write a function in your module/theme that will accept two arguments,  

1) the serialized value a:3:i:1;s:3:"First Subfield";i:2;s:4:"Second Subfield";i:3;s:7:"Third Subfield"; 

2) the name of the key you want to use. 

Have it return the value.

Create three new columns that use PHP code in your view,  and pass the appropriate arguments to your module/theme.