Question about case and participles

[philena.livejournal.com]

Hello,

If I want to say something like "I see the man who is reading all by himself," what case would I put on один? Would it be something like

Я вижу человека, читающего одного

Or would the сам need to be dative, as it sometimes is in embedded clauses:

Я вижу человека, читающего одному

Or are both correct? Or is neither correct? I am particularly interested in the case relation between the participle and один, so if there are better examples to illustrate it with, please let me know what they are.

Thank you.