It isn’t a limitation so much as a precaution. You’re not meant to have an easy time putting passwords in clear text :).
Read through some of the articles listed at http://powershell.org/wp/?s=credential, and you’ll see how others have dealt with the problem.
What you really want to do is set up a remoting endpoint that (a) lets users connect by using their own identity, which can be passed along automatically, and (b) run the commands in the session under a permanently saved alternate credential. If you look at “Secrets of PowerShell Remoting” (under Free eBooks in our Resources menu), there’s a chapter on doing what you’re after.