We are exploring options of adding SSL to multi-store (e.g., www.company1.com and www.company2.com).  To keep the cost down, instead of installing two SSLs for company1 and company2 respectively, we are thinking to create a third domain (e.g., www.company3.com) with SSL and direct all the https traffic from company1 and company2 to that secured domain.  For example, during the check out, company1 and company2 will be directed to https://www.company3.com/checkout/compay1 and https://secured.company3.com/checkout/company2 respectively.  Has anyone tried that before?