Well, if you have just the @v and @up, it's not the most ideal to create a spinning around v axis, because the orientation tends to get wonky when the v vector gets near the up vector. Either way, here's a poor man's setup I use:
//This method may result in fast flipping if the particles do loop-de-loops
//v@up = {0,1,0};//set this if you don't already have an up attribute
vector forward = normalize(v@v);
//create a quaternion rotating about the forward axis over time
vector4 rotQuat = quaternion(@Time*10, forward);
//use qrotate to rotate a vector by the quaternion
v@up = qrotate(rotQuat, v@up);
Using @orient is better because you don't have to worry about zero velocity situations or up vectors, but it requires some extra setup during the sim process (Assuming it's POPs)