No, you should still cast on loosely; even though it has 7% elastic in it it is still mainly made up of cotton, wool, and nylon. Also, you do not want to over stretch the elastic that could put more stress on it than you would like or need causing it to stretch out faster.
Judge: Madame, either you will have to cease knitting or I will have to cease judging. Which shall it be?
Miss Marple: It helps me to concentrate, milord.
Judge: It does not help me, madame.
Miss Marple: Oh. Very well. (puts away knitting)
Judge: Thank you, Madame.
The lyf so short, the craft so long to lerne.
~ Geoffrey Chaucer - The Parliament of Fowls Line 1.