Just don't keep using the dump button.
A few times won't hurt it just it's not recommended. Just like going past or very close to the redline. Sure you *could* do it but it's not recommended because it puts strain on the engine and you risk overheating and blowing it.
Something you can do is press it lightly and let a little bit of gas escape and then letting go and letting it sit (so the o-rings can unfreeze) and repeating until all the gas is out. Now I'm not sure if this will exactly preserve the o-ring however it makes sense that if you meter it out and do it slowly it shouldn't be as bad.
In aviation actually, the crappy sewage water/avgas/oil stuff is actually collected and metered out slowly so that it doesn't adversely affect the environment so I don't see why metering out your gas slowly using the dump valve should hurt it.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE