If he used ranged attacks, he would more easily get full attacks. One concept to do this is the "John Woo" rogue:gavagai said:its seldom he gets a full attack sneak combo
1) Use light light or hand crossbows in each hand (this allows for both TWF'ing and Rapid shot extra attacks)
2) If needed (for to get all your attacks from a high BAB) use quickdraw and/or rapid reload to cycle through the crossbows
3) Use permanently animated crossbows (multiples of these could be cheaply created with a single casting).
4) Have a party spell-caster caster greater magic weapon on one or two.
5) Ask if it can be used to launch alchemical items (i.e. for touch sneak attacks)
Have backup (trickster-type) tactics ready to still be useful here: Acid vials, holy water, spell-storing weapons, special material x-bow bolts, maximized fire trap 'grenades', shrunk boulders, UMD devices, buffs for allies, tan bag of tricks, dust of sneak and choking, etc.there are quiet a few CR 15 critters immune to critical hits.