[from occupied ga]

We would need to find and use some errant body that's going in that direction, much like bugs climb onto driftwood during a flood.

First off I think finding such a body would be an extremely low probability event. But, assuming you find one going in the right direction you have to have everything you're taking along match velocity with it. If it's going at a speedy clip then somehow you have to get up to the speed of whatever you're riding on otherwise you have the bug hitting the window of the jet plane effect. Then there's the problem of the other end. How do you slow down enough to avoid making a kinetic energy explosion dwarfing the size of the KT boundary event? I would say that the devil is in the details, but these aren't details. They're the major components of your proposal.

[amorphous]

Matching velocities is something inherent in either method. Using another body eliminates the need to accelerate tons, and tons, of mass for protection from cosmic rays, micro-meteors, and provides for subsistence, as long as this body had water and various other elements which could be mined by those aboard it.

That is if we wish to send people. If we only send DNA, in the form of some sort of organism (water bear, bacterium, or even viruses perhaps) then a lone craft of much smaller size would probably be the best alternative.