Is it possible to have extra kidneys or organs temporarily donated to someone healthy to last untill a recipient is ready?

No, because the organ undergoes stress even with a well matched recipient. And the new host has to take anti rejection drugs, but even then the organ may be rejected.

There are a lot more potential recipients than there are organs.

Even if @zenvelo‘s apt comments can be overcome, the answer is still no.

A doctor – at least in the USA and most of what we consider the developed world – signs onto the Hippocratic Oath before beginning practice: “First, do no harm.”

Cutting into a healthy person’s body – even with good intent for someone indefinite in the future – causes harm. Doctors can absolve themselves of that restriction when they cut into a healthy organ donor (kidneys, in particular, but now also liver sections as well, and mabye more in the future) to obtain a healthy organ for transplant. The thought is that it is a genuine life-saving (or hugely life-improving) operation to aid another patient that is known by the donor, so in this sense it’s a collaboration between the surgeon and the volunteer / donor to save the life of a particular person.

If the proposed implantation was “indefinite” for “no one in particular” and at “some time in the future”, there would be too much potential for abuse. I doubt whether any legitimate medical organization would sanction such operations, ever.

The Hippocratic Oath isn’t relevant. It isn’t binding. It’s aspirational and there are multiple versions of it.

Regardless, there are A LOT more recipients waiting for an organ than willing donors. For example, the average wait for a kidney in the US is five years.

If a living donor volunteers, the wait is zero years. There is no need to keep the kidney in some interim state of storage.