can i mention eloquent form comparator inline?

so .net 3.0/3.5 provides us lots new ways query, sort, manipulate data, interjection neat functions reputed linq. sometimes, i need review user-defined forms don't have built-in comparison operator. cases, comparison unequivocally rudimentary -- something foo1.key ?= foo2.key. rather formulating new iequalitycomparer type, i simply mention comparison inline controlling opposite delegates/lambda functions? something like:

var f1 = ...,
    f2 = ...;
var f3 = f1.except(
           f2, new iequalitycomparer(
             (foo a, foo b) => a.key.compareto(b.key)
           ) );

i'm graceful certain above doesn't indeed work. i only don't wish have something "heavy" whole category only tell way review apples apples.