You have linked the relevant official request for this in your answer and SERVER-3748 does explain some of the reasons why these don't currently exist.
The most basic reason is that you cannot start
mongos without at least one config server being up and working, otherwise it will refuse to start, which makes it a poor candidate for an init script (external dependencies). Generally you want to avoid having services that are going to fail to start when there is no good way to check the reason for failure.
However, it would still be beneficial to give people a script rather than having them modify/write one themselves, hence the Jira issue exists.
The way I would recommend to do this is to base any script off of the existing
mongod init script and simply modify it to replace
mongos where appropriate. Here is the current version of that script for Debian:
Things you will need to change:
The advantage to doing this, after you have installed the 10gen package, is that the users will already be set up and you have the
mongod script for reference on the system.
You will need to create the config file with appropriate values for your mongos, and there might be a couple of other things you need to tweak - the key is to test before you make anything permanent.
Once you confirm via testing that you have the script working as you wish, then you can add it permanently with