Hi,
Well, you could duplicate these payment methods in the System>Payment methods menu and have the copies with a "percentage value of -50 so that it would remove 50% of the order total value as "payment fees" and then use a translation override to rename "payment fees" as "deposit option selected" or something like that.
www.hikashop.com/download/languages.html#modify
However, this means that the total order value will appear as 50% of the real total amount and thus once the payment will have been made for the 50% of the value of the order, the customer won't be able to pay for the rest of the 50%.
You would have to manually create a new order for the customer in the backend to have him pay the 50% that are still unpaid.
Another option would be to modify the payment plugins to handle all that automatically (charge half the amount at the end of the checkout, and then charge the customer the rest). But that's a lot of customization work and you have to do it for two payment plugins. If you're a skilled developer and you have some time in front of you that's possible, otherwise, I wouldn't recommend trying this.