I need to set an environment variable for a command that is being called via nice. [Bash and dash, Slackware and FreeBSD.]

 $ JIM=20 nice -n 10 echo $JIM $ 

Nope, echo can't see JIM

 $ nice -n 10 JIM=20 echo $JIM nice: JIM=20: No such file or directory $ 

nice don't like it.

I can export JIM and then echo can see it, but now I'm polluting the environment. Unclean!

I tried the "--" option to signify end of command line variables for nice, but it makes no difference, nice complains. I can't believe no one has wanted to do this before, so I'm probably making a very basic error.

Any ideas?