I'm just trying to get into raking during playing to add more of a dynamic feel to my playing and soloing...

I've been using riffs in "rude mood - SRV" and "say what - SRV" but when it comes to raking and letting notes ring on the g,b and e strings I find it harder. I play using the SRV-type baseball bat grip with my thumb wrapped round the low E. When raking and letting the bottom notes ring, i.e.:
5 8 x
x x 7p5
x x x
x x x
x x x
x x x

I find it much harder to play the above without using the normal "thumb propping behind neck" grip.

Also, does anyone have any good drills for practicing raking, particularly with little two string chords/embellishments as I find this hard aswell.

Thanks in advance guys!
You could always use your palm on your picking hand to mute the lower strings above the note you are playing instead of using your thumb.