For all practical purposes, you can get the same effect by passing the input argument back out. For example, in the function definition:
function myVariable = ChangeMyVariable(myVariable)
myVariable = 2 * myVariable;
Then to call it, do this:
myVariable = ChangeMyVariable(myVariable);
And, obviously, myVariable could be anything, such as a structure like you mentioned. For all intents and purposes, this is the same as the code you'd use if it were pass by reference:
The net effect is you get your variable changed, it's just slightly different syntax.