Ok, this is how I solved that.
I had to edit rptdesign file and change oda-data-source element
I changed extensionID to extensionID="org.eclipse.birt.report.data.oda.jdbc" and left only odaURL pointing to nowhere and added odaJndiName referencing to my jndi datasource java:comp/env/...
Looks like someking of hack...
Why does MyEclipse Reports Wizard create data sources with that nasty extensionID="com.genuitec.eclipse.reporting.oda"? Why not generate datasource with standard BIRT datasource?
I general - I'm kind of disappointed in MyEclise Reports... My part was only to solve that datasource issue, and to me MyEclipse Reports is totally immature and not ready for real produciton... who on earth is using hardcoded jbcs connection urls?!