How to pass a LINQ query to a Sub and filter it?

[axplains]

Hello, I have a LINQ query:

Dim Db = New MyDataContext
Dim Qry = From cust in Db.Customers
     Select cust.ID, cust.Name

And I want to pass it to a function to filter it, like this:

FilterQuery(Qry, ID)
...

Sub FilterQuery(ByVal MyQry as iQueryable, MyField as ???)
  MyQry = MyQry.Where(MyField = "somevalue")
End Sub

How can I pass "MyField" to the Sub and make the LINQ "Where" clause work?
Is there any workaround?
Thank you.