The new line <br> tag is added by design as a separator and it t puts the text of the each subsequent textbox on a new line.
Your approach is OK and you can implement it.
Another approach implement a custom text source and you will be able to set the content that you want to check: http://demos.telerik.com/aspnet-ajax/spell/examples/textsource/defaultcs.aspx
All the best,
the Telerik team