Lighting, Light Fixtures, Ceiling and Exhaust Fans - New light ficture on a 3 way lighting

I need help on installation. I have a light in the basement stairs with a three way switch. 1 switch upstairs and 1 switch downstairs. I want to add another light on the upstairs and I only have access to get power on the upstair switch. The switch has a red/black/white wire. How can I connect the wires so they all work together.
Let me know if it's clear or you need more details.

Thanks in Advance

You cannot. It's impossible.

The only sure-fire way is to run a cable from the exising light to the new light. It also might (but might not) be possible to do this with a cable from the downstairs switch to the new light, but that would depend on other factors that we can explore if you want.

I know that currently you think that you only have access to the upstairs switch box. But a book on home wiring will provide a lot of tricks for fishing new wire. Even if that fails, read a book on drywall repair. It's not rocket science.

Thanks John, I was afraid of that. I was trying to avoid all the drywall repair that I need to do but since I'll be renovating my basement I will add this to the project.
As for fishing wire elsewhere, it can't be done. I need the 2 lights to open/close at the same time and from the same switches.
Thanks for saving me the headaches trying to figure it out.