Hi!
This is a bit off-topic, and somewhat blatant self-advertising, but for what it's worth, we developed a method -- preparing it for publication, draft going on biorxiv soon -- to deal with single cell RNA-seq without ERCC spike-ins.
Here's some info on it
http://genestack.com/single-cell-rnaseq/ and a bit more here
https://genestack.com/blog/2014/09/2...ysis-tutorial/.
The method is available on Genestack.
--Misha
P.S. I'm the founder of Genestack, happy to answer questions etc.