How should I do this?

[Zagen]

I actually think Dagger is MORE useful than Marksmanship these days. Especially for someone who already has capped dagger on DNC (and likely has merits too). With good options like augmented Yataghans (my best has DMG+8/Crit+3% augments) and Twilight Knife and solid melee gear, COR isn't bad with a dagger. I find it better than the subpar damage and extreme cost of shooting for TP. As for WS, Leaden Salute and Wildfire are magical WS which are not affected by Marksmanship skill. And Evisceration is arguably better damage than Slug/Det both inside AND outside of Abyssea (not to mention cheaper since you're not using ammo).

Melee DoT takes a huge hit from buffing even more so now if you strive to sit on XIs. Lower Marksmanship Skill also makes your Quick Draw essentially useless which means no helping on sleeps, dispels, or boosting elemental WS damage/dealing instant 200+ damage. Also the only event that a COR is really helpful in currently is Voidwatch and from what I've been reading COR is great because the buffs are needed and they can dish out ranged damage allowing them to stay out of AoE range, this can't be done with a dagger.

I don't know a single THF or DNC who will agree with you about evisceration being a better dagger WS outside of Abyssea, let alone better than Slugshot/Wildfire.

As to the concern of gil that should be a non-issue if it is there is a problem. Between Sea Daughter and the fact that a decent EXP group inside abyssea runs at least 100k Cruor/hr which converts to 250k gil you should be making a good profit just fro EXPing. You make even more gil if that group is doing Dominion Ops with the gil you could get from the augmented weapons(6.5-7.1k).