Would
Lewis be out of the question? And why not
Meriwether as is? If it's to "out there" as a first name, then as a middle name it's fine -- more than fine. Or, did he have a middle name that could work?
Clement means "mild" as in "mild / merciful." That's a tern that is also used for (good) weather. A combination like
Clement Eugene would get close to the meaning of
Meriwether. Sort of.
The only other thing that came to mind was
Meredith, which is traditionally male. But at that point you might as well stick with
Meriwether.
Sorry I'm not much help. Basically, the best / safest way to honor the explorer in the first name slot is to use
Lewis. :0)