Hello,
Yes it is be possible to create LEP functrionality within APP stylesheets. Native APP would be easier, but it should be possible with source edits and/or template associations.
There are many variations to what individual customer LEP requirements are so it would depend greatly on this and your content structure.
We have studied this for a customer with with DITA and it is cirtainly feasable, with a little hands on work.
Regards
Chris