You can use something as simple as gelatin or infused milk (heat up the milk and whip using a hand whisk or a cheap cappuccino whipper) or mix an emulsifier such as Xanthan gum or soy lecithin. Use about a couple teaspoons per couple cups of liquid and mix using an immersion blender. The sort of foam you will obtain from this is relatively unstable and is only good for rapid service.
An alternative is to use a product called versawhip, which when simply whisked into the liquid will allow it to be whipped as if adding an egg white powder. Syrups combined with versawhip will whip up to a consistency similar to meringue.
"If it's chicken, chicken a la king. If it's fish, fish a la king. If it's turkey, fish a la king." -Bender