At level 28/32 you can put points in DEX too but itīs not necessary. At level 15/18 you can chose a free feat, take 'Shield Proficiency' if you want a better AC or 'Ambidextery'/'Two Weapon Fighting' (unfourtunately thereīs no room for 'Improved Two Weapon Fighting' until level 36 ).
Never played this char so I donīt know if heīs any good but heīs really a Master of Defense.
If you want to start with DEX 18 (because your char is human for example), you could take Self Concealment V at level 36 (and because of the extra feat at level 1 you can take all the three dual-wielding feats). There are a lot of other builds around rogue/HS/epic dodge/self concealment. You can drop the SD for example, take more rogue levels and add fighter (or champion of torm).
Also donīt underestimate the epic Harper Scout. If you want to maximize dextery (or charisma) thatīs the way to go.