In theory you can make your own installer though. In a nutshell by:
1) Checking latest version number (use the Update URLs for that)
2) Use that number to create the proper URL to download all the needed packages from the Plus! servers.
3) Install all those packages by unpacking and then copying the files to their proper maps, and others by initiating the proper installer (like the virtual webcam driver).
Of course, more specific checks need to be done, like checking of the current installed version, the used paths, etc...
It's certainly not impossible (though it would be against the terms of usage I suppose) but it requires some serious checking and all and it does have caveats. For example, if they change the Update URLs or the URLs of the packages (or the amount packages) your installer wont work anymore.
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A better (and much easier) possibility is to use the still existing
/destination and
/silent command line parameters.
Execute the setup with the /Silent command line parameter.
A different installation path can be specified with the
/destination parameter if you wish to do so.
eg:
PlusSkypeSetup.exe /Silent /Destination=C:\PlusSkype
(small downside is that you can't select the default language.... but that could be solved by setting the proper language either in the preferences of Plus! or either directly in the registry)
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