We will introduce the ability to set different borders (left, right, all etc.) with different colors in the official release of the Spreadheet control, which is scheduled for the Q1 2016 release in mid-January. Unfortunately at the moment we are not planning to introduce the ability to set border weights, however you can log this as a feature request in our public feedback portal:
Currently setting the border for 1000 cells takes less than a second.
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Feedback Portal
and vote to affect the priority of the items