Liferay + Vaadin multiple different versions

is it possible to use different Versions of Vaadin in one Liferay installation?
This case is real when developing multiple portlets that are done by Vaadin way. One portlet is for example done using version 6.4-custom and second one is using verison 6.6. In real wordl we don’t want always upgrade old portlets that works well. But as Vaadin is used by liferay portal itself then as i understand all portlets must use the same version. Am i wrong?

Thank you