you can use any browser to download Spark using the URL Spark Manager does provide. So it shouldn’'t be a problem to put the file to another server, but somehow Spark Manager must be accessed by the clients to check if a new version is available. You may use mod_rewrite and mod_proxy as described here: http://www.jivesoftware.org/community/thread.jspa?threadID=18516
I don’‘t use the Spark Manager but it seems that it is not sending HTTP Location: URL’'s so there should be no problem.