Merrick here...

If you've seen the TR2N teaser/demo real (either at Comic Con, or via its subsequent leak across the Internet), you got a quick glimpse of Jeff Bridges reprising his Flynn character from the first film. And, you would've noted that two incarnations of Bridges were featured in that sequence: Bridges at his current age, AND Bridges appeared in the 1982 film.

Here's a look at what I'm talking about:

IO9 has a quick article about os this is being accomplished:

A source reveals to io9 that Jeff Bridges has been sent up to Canada to be digitized. A plaster cast has been created of Bridges.

Our tipster tells us that:

They will then take that 3D model and make him younger and then slap it on a body double in post.
As this is only one cog in the machine, I can't give a whole lot of detail. Canada scans actors and props to be used for various projects. These are very high resolution scans that pick up every wrinkle, face lift and scar on the actors body.

...says the piece, whose entirety can be found HERE.