No, AFAIK you can’t. I mean, you can define a generic closure, what you can’t do is create a let binding with a generic left-hand side.
A fn get<T>, as the one you mention rewriting, undergoes monomorphisation, i.e. when compiling it, rustc generates a different version of get for every actual T that is used to call it. By the time you assign the result of that get (let a = get(...)), that result has a concrete type and size.
A let binding does not get monomorphised, so you can’t have a let a<T> = ... and have a different version of a generated for you by the compiler.
What I think might enable this is the introduction of higher-kinded types, which is one of the highly desired but not yet fully fleshed out new features for Rust. They would enable you to write something like:
// does not work as of Rust 1
let a = for<T> |s: &str, t: T| {...}
i.e. return a closure that I can later parametrize with a T (which is what you’re asking for).