To put it in perspective, a typical starter when loaded (cranking the engine) pulls somewhere between 160 to 250 amps. On the other hand the solenoid that is holding the contacts in that circuit closed draws between 10 and 30 amps. That is why the cable from the battery to the starter is such a large cable; it is carrying HUGE current during starting.
That said is it certainly still beneficial to get the 10 - 30 amps of solenoid current off the small ignition switch contacts by adding a conventional Bosch cube relay in that circuit. But is it a starter solenoid relay, not a starter relay.
There I feel better. I've ranted and most all of you are probably saying yeah, so what get a life.
is a better idea than jumpering the contacts or doubling the wires. How much benefit you get from jumpering the contacts depends a lot on how you do it. You have very low resistances (say 1 milliohm per connector for contact resistance and 10 milliohms in a 10 foot 10AWG wire). It doesn't take much resistance in that scenario to shift most of the current one from one contact to the other. A poorly crimped connector with 5 milliohms of resistance might move 80% of the current onto the other contact. Even if you manage to balance the paths perfectly so that the current splits 50-50 you're still moving a lot of current through the ignition switch contacts (and now two of them at once).