Not sure I got you here. Indian govt.'s foreign policy with SL is shaped by two elements.
1. Central govt.'s fear of TN asking for separation - it is a knee jerk reaction on part of Central govt. based upon some voices in 1940s and 1950s.
2. Indian govt.'s fear of US and now China using SL as its base to unsettle India in the South while we are facing Pakistan/China in the North.
With respect to the first one, it is upto the TN people to lay that fear to rest - We had lost Katchatheevu due to this reason and now our fishermen gets killed. This will give rise to a more robust foreign policy with SL. Rajiv Gandhi is one person who had the vision with respect to dealings with SL.
And again to address the second one, it does not take much except the onus in still with TN people. TN people need to elect only those who represent Tamilian interests and not morons like Karunanidhi or politicians like Jaya who does not understand it. With coalition politics, it becomes easy for the TN leaders to take into consideration Tamil people's interests rather than the eternal bogeyman. SL is not stupid to allow a base for US or China and even if they allow, it is not going to lost longer as they do not want their independence compromised in anyway. Also they very well know what India is capable of based upon the past 50 years experience.