Can I call the encrypted exe-file with the password as a command line parameter.

Yes. You can call it with the following format:
"ep[####]" ( #### is the password. ep[] must be included as a part of parameter.)
C++ Example ( "google" is the password.):
WinExec("c:\program.exe ep[google]",SW_SHOW);
or
ShellExecute(Handle, "open", "c:\program.exe", "ep[google]", NULL, SW_SHOW);