How to migrate MOSS 2007 custom site themes to SharePoint 2010 ?

Hi All,

We have an application developed in MOSS 2007 wherein there are 20 custom  site themes created and we are migrating that application into SharePoint 2010 , so how can we migrate MOSS custom themes in SP2010. As I had gone through couple of blogs mentioning that the theming engine is entirely different between Sharepoint 2007 and 2010, so themes from one don't work in the other. I tried the option of using MS PowerPoint and theme builder but that is not the workable solution for me. 

is there any way that we can convert MOSS custom themes in .thmx format that SP2010 works? or can CSS files converted into .thmx format ?

Any help would be greately appriciated.

Thanks,

Dhananjay.