If you want to put a surfactant blend into a foamer bottle, in general, you'll want to add double the amount of water to the mix to make it very watery. So if you have 100 grams of product, you'll want to add 200 grams of water to the product. Mix very well, and add to the foamer bottle. Easy peasy, right? No, wait, we're missing something. We need to add some more preservative to the mix to make sure it stays nice. We have enough preservative in the product for 100 grams, but not for 300 grams. So add your favourite preservative at the recommended amount - mine would be liquid Germall Plus at 0.5% for a total of 1 gram more - into the water and then combine together.
Having said this, when you dilute the cleanser, you dilute those ingredients we've added to be great for our skin. So instead of having 2% hydrolyzed oat protein, you now have 0.67 grams of oat protein, which is going to feel different on your skin. If this concerns you - and I know it would concern me because I've put in the effort to research and include some lovely ingredients in my cleansers - then you'd want to scale the recipe to include more water and keep those ingredients at good concentrations. (Check out the recipes to which I've linked below for more ideas...)
So there is a slightly easier way to do things...don't add the thickener to the cleanser. In general, our surfactant mixes tend to be quite watery before we add in the Crothix or glycol distearate or other thickener, so leaving out the thickener means it might be thin enough to put in a foamer bottle. Try this approach first, then diluting it with water to get it into that bottle!