Go to an place where there are white elephants. Bring with you a muffin (with raisins).

Climb a tree. When the white elephant is close, drop the muffin (with raisins) in front of it.

The white elephant will be happy, and eat the muffin (with raisins). White elephants like muffins (with raisins).

Repeat this procedure for five days in a row. After the fifth day, the white elephant will be used to its daily muffin (with raisins).

The sixth day you climb the tree, bringing with you a muffin (without raisins). Drop the muffin (without raisins) as usual.

When the white elephant finds out that the muffin (without raisins) lacks rasins, it will darken in anger.

And then you catch it the same way you catch an ordinary grey elephant.