Trying

There is a famous teshuva of Rav Yaakov Emdin Z”l specifically permitting a sheitel proving that it is covered – at least partially.

http://hebrewbooks.org/pdfpager.aspx?req=1408&st=&pgnum=36

In fact, a talmid of his wrote back trying to get him to clarify or retract his p’sak and there is another tshuva later on to this talmid where he reiterates again clearly that it is permitted just like a piece of jewelry.

You might also want to enter a search for “Peah Nachris here: http://hebrewbooks.org/advanced.aspx

That’s a lot of material…