Belgium embassy doesn't issue these letters, they write it on their website ( you still can explain them your situation and see what they say, but I wouldn't count on it) , so I guess the only option you have is to go for the yearly extension like Tod said.
However there have been people who got told by immigration officers that they are under the visa amnesty when they went to apply for a 60 day family exstention. Contact your immigration office and ask them.