Don't run installation, just copy all executable files from another machine to any directory (You even don't need all files, but we will skip this part for now). You cannot write to "Program Files", so a good place to put all files is "C:\Users\Public". This directory is shared by default to everybody, so, if network sharing with default settings is enabled, you also will have physical access to files via network. I like to create "C:\Users\Public\Programs" directory, with "Boinc" and "BoincData" subfolders. This could be done remotely via network, if public/guest sharing is enabled.
C:\ProgramData is second solution, this directory is writable with user privileges (but no network access). Of course, you could create any directory on any drive, but this is more noticeable.
Note: I don't recommend to use pathnames with spaces, boinc have some bugs handling this (at least in "detach_console" option).
The installation could be verified by running "C:\Users\Public\Programs\Boinc\boinc.exe --dir C:\Users\Public\Programs\BoincData". Use normal user account. This will initialize data directory as well. Ctrl-C to exit.
Managing: nothing special, just read boinc documentation about remote management. In short, you must create "remote_hosts.cfg" (pre-copy it to the data directory) and put password into "gui_rpc_auth.cfg" (either pre-copy your own either get random one which boinc will create during directory initialization).
Creating a service: from elevated command prompt (run as Administrator), enter following command exactly, with spaces and quotes as here:
sc create BoincSVC start= auto error= ignore binpath= "C:\Users\Public\Programs\Boinc\boinc.exe --daemon --dir C:\Users\Public\Programs\BoincData" depend= "+TDI/+NetworkProvider" displayname= "Berkeley distributed infrastructure"
(You may edit service name and displayname if you like). Note the space after "=" (quite funny syntax).
Checking for user activity: in Windows 7, when Boinc is run as service, you must somehow also run boinctray.exe utility which will do real check for activity and report this data to service (don't worry, it does not have tray icon regardless of name). Use regedit to create Run-entry.
Unfortunately, I'm not completely sure how to run it correctly. If there is only one user on this system, a way which surely works is to put this under HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run branch. Create new string entry with any name (e.g. "boinctray") and value "C:\Users\Public\Programs\Boinc\BoincTray.exe". If will run as soon as user logs on. If there are multiple users, I'm unsure. May be HKEY_LOCAL_MACHINE\Software\.... will work, may be not.
Now boinc service knows about user activity and all settings from venues (e.g. pause if computer is in use) will work.
Theoretically, last two steps (sc and registry update) could be done remotely if you know Admin's password AND have Admin account enabled and available for remote logons, but my knowledge is not so good in this area.
Note that boinc.exe itself really does not require any registry entries. It's looking only for default data folder, which we'll specify on command line.
Optimization of the procedure described above (using a batch file or custom .msi) is up to you.