Five Guild Alliance Scattered...

[Dharkon.6481]

I feel like this is more of a need for you and your large gaming society to restructure your guilds based on the interest of your members.  You could do a number of things.  You could convert one or possibly two of your guilds into flagging guilds for wvw interested members, or you could create another "host" guild just to allow members to join it whenever they feel like they might want to get their feet wet in WvW.  You wouldn't be able to even fit 500 people into one side of a WvW matchup at once even if you covered all four maps with your members.  There are options out there to help your guilds enjoy WvW restructuring, you'll just have to take some initiative to make it work.