During installation, open the software Miranda, bring the password window to the desired state (clean from unnecessary controls and rename). The user enters the password, Miranda saves it in the config. Then you kill Miranda.
You can run the already installed instance, you can create a temp folder and put in her version of Miranda without ryushechek, and then copy the config to the right place. This option is good because then if you need to rebuild the installer for the new version, you will have trouble.
Don't forget to protect yourself: when set to show a checkbox "do not enter a password right now." If for some reason doesn't work, the user will be able to install Miranda without the introduction of login and password.
Yes, Yes, Yes, I know what a disgusting crutch :) Use it only when options are not left at all.