Hey, long time member here.
Been asking for a while for a profile plugin to allow me to put what info i want from linkedin in to the user tables for a custom component and you mentioned you were going to be doing this, any news yet on this?
We recently created a plugin like you're looking for. It only will work with the upcoming JFBConnect v5.1 release, but should work with recent JLinked versions (though we haven't tested that yet).
The plugin code isn't very complex, but what it does can be very tricky. Right now, it can save into either the Joomla database or an external one and can write into 1 table. That table must have 1 row per user with columns for the fields you want to save. There must also be a row that will either store the user's Joomla User ID or social network User ID.
I'm not sure when we'd fully release the plugin as there's still some rough edges and possible difficulties in configuring, but we'd gladly give it out to you to use/test and get feedback. However, I'd prefer to wait until v5.1 of JFBConnect is out give it out, so I actually have time to investigate/fix any problems you may have.
In the meantime, let me know if the structure of your user table would work with the stipulations above, or if you'd need it to work some other way.