Never tried it before but im interested to try it out. Depending on your age really, find out how many HJs you can do a week and still function normal. Then do half through out the week then go for your anal.
Problem is if you HJ too much you might find yourself lasting too long and not unloading at all. Due to desensitizing the nerves to touch.
Another method is buy yourself one of those fleshlight type toys if you want to spend the dollars. It's gentler on your tool and to build up your endurance too. Just make sure find the hasher thread type for endurance.