Here you go, edited it some to remove some of the custom stuff we do here, but it should get you in the right direction:
#!/bin/bash
extName="ublock.safariextz"
extPath="/Users/$currentUser/Library/Safari/Extensions/"
packageExtLocation="/tmp/"
tccPath="/Library/Application Support/com.apple.TCC/TCC.db"
sqlite3 "$tccPath" "INSERT or REPLACE INTO access VALUES('kTCCServiceAccessibility','com.apple.Terminal',0,1,1,NULL,NULL)"
sqlite3 "$tccPath" "INSERT or REPLACE INTO access VALUES('kTCCServiceAccessibility','/usr/bin/osascript',1,1,1,NULL,NULL)"
sqlite3 "$tccPath" "INSERT or REPLACE INTO access VALUES('kTCCServiceAccessibility','com.apple.loginwindow',0,1,1,NULL,NULL)"
# Give it some time to process..
sleep 1
# Now we're going to mess with UI elements. First we open the Extension, which initiates copy to ~/Library/Safari/Extensions/
# Then we're going to tell Safari to hit the Trust button, which creates the encryped keychain entry
# Then we close the Preferences Window by using Command + W.
osascript <<END
tell application "Safari" to activate
delay 1
tell application "System Events"
tell application process "Safari"
set frontmost to true
tell application "Safari" to open location "$packageExtLocation$extName"
delay 1
click button 1 of sheet 1 of window 1
keystroke "w" using command down
end tell
end tell
END
