I've collected extra runnings, and then put them in Ziploc freezer bags and just froze it.
then thaw, boil to make sanitary and then make the starter.
this works fine especially for short term storage (a month or so). after that mine got freezer burn crystals.
Primary: English Mild
On tap: Pale Ale, Lancelot's Wheat, English Brown Ale, Steam Beer, HoovNuts IPA
Bottled: MOAM, Braggot, Raspberry Melomel, Merlot, Apfelwein, Pyment, Sweet mead, Cabernet
Gal in 2009: 27, Gal in 2010: 34, Gal in 2011: 13, Gal in 2012: 10