>>There was a neat old trick for this on slow networks: make the exe read-only. It's not network access per se that's slow, it's the checking for locks. Since nobody is changing the exe (but the installer), setting it read-only will just tell the network not to bother with locks.
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>Is it enough to have the exe on a readonly drive (or in a readonly folder) or must the file itself explicitly be readonly?

Didn't try any but the last, so I wouldn't really know.