You should design a UserVoice switching tool that would allow current UserVoice customers easily switch to UserEcho and import their existing feedbacks threads and if possible, user account details. This may make it more appealing for prospective customers to switch over to you.
I am thinking of the OpenID foundation whom are currently using UserVoice but I am lobbying them to switch to UserEcho, although they already have some valuable feedback threads in their current UserVoice forum which they would want to save.
My lobbying here http://ideas.openid.net/forums/252-ideas/suggestions/1891667-switch-from-uservoice-to-openid-supporting-userech
and my suggestion for you to also approach them here http://feedback.userecho.com/feedback/41338-approach-the-openid-foundation-to-provide-feedback-for-their-site/