Psion is a good idea - if you can use hyperconsciousness, then you can also use persistent power. Add that in with overchannel, and you can persist 6th level powers. However, even with only 3rd, that is a lot of persistent detection (including touchsight).
This is a sherlock build I made that was not a primary caster:
BuildFactotum 3/Human Paragon 3/Marshall 2/Jordain Vizier 5/Heir of Syberis 3/Chameleon 2/Crusader 2/
FeatsAble Learner, Keen Intellect, Iron Will, Spellwise, Leadership, Dreamtelling, Ancestral Relic, Heroic Spirit, Investigate, 2 more, 1 floating
Notable Powers"Take 11, Int bonus to most skills/things, 2 minor auras, Eidetic Memory, Moment of Precience, Dreamtelling, etc.
- Perhaps take Changling feat rogue 2?"
Some useful stuff:Changling Rogue Substitution Level
Jordain Vizier's Eidetic Memory ability
Dreamtelling
Hypercognition (or even just Moment of Precience)
Sponteanous Divination ability for a wizard
Here's a diviner wizard I built:http://brilliantgameologists.com/boards/index.php?topic=365.msg7186#msg7186Some random thoughts.
Best,
David