I guess you can..
First of all - Nude Patch, available to download for free. But this one is for bathroom and for hot tub if your sim is friendly enough.
Or.. if you have The Sims 2 Body Shop (also available) you can try to make underwear look like sim's skin, and that would be that type of outfit that you want it to be, even formal :))
Or.. download anything you want from the section Sims 2 adult content from special websites :))) watch out for viruses!!!!

yeah but not without the pixlation but you must be pretty perverted to do that or you have some weird desire to create naked sims
thats just porn man just porn