Well, since no one else is replying... There really is no way to do it that is not subpar. Although I don't think it would take a lot for the devs to make it competitive. An imbue (even a weak one) and/or some sneak attack, have Tier 5 enchant your weapon combine all three choices and give a HP bonus, add melee and ranged power in the cores... for a start?
Disclaimer - The following is not a complete build, but the beginnings of a thought that may become an idea......
That being said, a while back I tried to come up with a build that would work. The best I could come up with was a 1-20 past life getter simply to mix things up. However, what I would do today (if I was going to do it) is something like a 10 rogue, 6 wizard, 4 fighter. You could also do Dark Hunter instead of rogue and Dragon Lord instead of fighter, but those are a bit different.
Play style is SWF + Orb and max Intelligence with spell buffs and some CC.
10 rogue for sneak attacks, evasion, traps, and special ability to take advantage of high intelligence and Harper harper skill buffs.
6 wizard for 2 bonus metamagic feats; 3rd level spells which include haste and displacement and you will be taking Extend in Harper T5.
4 fighter for 3 bonus feats and access to Kensai
Feats would include (7 general, 3 fighter, 2 wizard for 12 total): 1) Insightful reflexes, 2) Improved Shield Bash (works on orbs), 3-5) 3 SWF feats, Improved crit, 6) Offhand versatility, 7) Quicken, 8) Precision. That leaves 4 more to play with depending on your weapon. But I would probably get Stunning Blow so that I could get situational usage out of Moment of Clarity (Harper T5). I'd also consider Improved Feint.
Enhancements (assuming Harper capstone, although I wish it gave +10 melee and ranged power).
Harper 41
Kensai 4 - haste boost (you will need it for this build); 8 for +3 to tactics
Eldritch Knight 11 (at least) - elemental Imbue, defensive buffs, and help with arcane spell failure
Feydark 11 - This is for Greater Color Spray for extra CC. Should work good enough on low reaper and even better with Moment of Clarity. I think
Greater Color Spray is a level 5 spell, so heighten won't help it.
That is 67 AP or 71 with tactics.
In a nutshell, this gets you a Battle Trance and Haste Boost along with an extended Haste Spell, but you do not get a critical multiplier and a major issue is that there is no Hit Point bonus in Harper Tier 5.
So that is what I would start planning with. If you have any specific questions, I can try to answer.
Cheers
