I read this paper in Plos One some time ago (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2773934/). This a very effective and inexpensive way to isolate plasmid. It is cleaner that column recycle. But if you want to do it, just wash the column three times with 500 ul of ultrapure water, repeat the operation with ethanol 75 % and again with water. Dry the columns and they should be OK. Do not use them more that three times. I hope this helps. 

We use 1M HCl. Please find protocol at : http://www.biotechniques.com/BiotechniquesJournal/2007/February/Regeneration-of-commercial-nucleic-acid-extraction-columns-without-the-risk-of-carryover-contamination/biotechniques-41235.html