useMutation does not allow late variables with typescript

Describe the bug

In the docs it's stated that you can either directly pass variables to useMutation or pass them once you call the resulting mutate function.

With Typescript, as soon as you specify two type arguments to useMutation, it expects you to pass variables directly to useMutation. It does not allow adding them later, which seems to be a bug to me.

Also, if you just supply one type argument to useMutation, the parameter variables of the resulting mutate function is undefined, not allowing any kind of variables. (Which is expected and correct, I guess)

To Reproduce

import { createComponent, ref } from '@vue/composition-api';
import { useMutation } from '@vue/apollo-composable';

type LoginMutation = {}
type LoginMutationVariables = {
  variable: string,
}

export default createComponent({
  setup() {
    // FAILS HERE: Expected 2 arguments, but got 1.
    const { mutate: login } = useMutation<LoginMutation, LoginMutationVariables>(Login);
    
    // Require variables here, since they're not passed before? Not sure if possible.
    login({
      variable: 'Hello World',
    });
  }
});

Expected behavior

Allow useMutation with 2 type parameters to accept variables at a later point.

Versions
vue: vue@2.6.11
vue-apollo: vue-apollo@3.0.2
apollo-client: apollo-client@2.6.8

Start at the TypeScript definition and overloads for the useMutation entry point, then reproduce the example with two type parameters. Check how variables are typed when passed to the returned login function. Done means the shown late-variable call type-checks while preserving the documented direct-variable usage.