LINQ to SQL and Dynamic Queries and Expressions?

Continuing my experiments with LINQ in the middle tier I ran into another problem: Inability to make LINQ run any dynamic operations that are not defined explicitly in the LINQ to SQL import. For building a generic business framework that doesn't have concrete type references (to say a PK field) but dynamically needs to create SQL to query data. Even relatively simple things like retrieve a single record by primary key where primary key is dynamic not explicit is not easily accomplished without getting real low level into Lambda expression creation.