In the UK, women are to curtsy before the King or Queen; but, what if a woman is wearing pants or slacks?

This is from Etiquette Lessons: Girls & Boys at the Table Teens at the Table. I imagine this would suffice for royalty.

...or if you are wearing slacks, raise both arms out to the sides to keep your balance. In one smooth motion, shift your weight to the left leg, bend you knees, tap your right toe behind you, lower your eyes and nod your head.

http://books.google.com/books?id=UhvOvTvdgFYC&pg=PA31&lpg=PA31&dq=curtsy+wearing+slacks&source=bl&ots=ytM8iTeoSt&sig=omfEE1Rq_4AZHdfMvMmZbbteyZ8&hl=en&ei=ph24TY2JIOPiiALw440b&sa=X&oi=book_result&ct=result&resnum=1&ved=0CBYQ6AEwAA#v=onepage&q&f=false