Hi, Yes its possible now.Very recently even i was wandering all over Internet
to get the answer to this question. And luckily i found the solution to this.
There is a site
WAREWORLD.CO.CC this site provides .SIS to .JAR converter and best part is its free.
The is a beta version. But who cares as far as it solves the purpose

it worked for me. Hope it will work for you as well.