I think it would be worthwhile having an EwayHostedPayment Class to avoid the hassle of needing SSL certificates.
I'm surprised the Class wasn't available with the EwayXmlPayment Class since appears to be derived from the source provided by Eway themselves.
Eway have a php download for EwayHostedPayment. Needs a little manipulation for Silverstripe.
http://www.eway.com.au/_files/samplecode/sample_php4_or_php5_shared.zip