Step 1. Distract your vasari opponent with a more pressing battle he needs to micro, skip this if it's the AI.
Step 2. Jump in 1 siege vessel and whatever your race kills SBs with (1 migrator, 3ish or more Ogrovs, whatever the hell advent uses)
Step 3. Kite the siege frigate in an 8 pointed star around the grav well, 3 revolutions should be enough.
Ta da! The vasari sb will follow the siege frigate around forever, never catching it, ignoring the shooting it's getting up the rear. It'll target stuff once it gets in range, but not with all cannon and you have plenty of time to build your own vasari starbase and chase it with your deflector running while you get your other upgrades. The ogrovs never actually come in range.
If the opponent catches on and targets your constructing SB, congrats!, jump in your spare migrator. if he targets one of your ogrovs, kite it and let the others follow behind the sb. As long as you keep him from microing the sb, you're gold.