Hi,
I've actually used one of these, but i used it for a dummy load to test something else so it did not get the full voltage it normally gets when used as a hair dryer.
The thing is though that these get very very hot, red hot in fact. And they usually have a fan installed that keep air flowing through the coils and that keeps the temperature down while also forcing the hot air to flow outward where it can be useful. So one way to use it would be to force air through it as it normally would be used, and just direct the hot air to whatever has to be heated. That way you dont have to try to 'overcome' any safety devices built in to prevent fire.
If the moving air is objectionable (in some heating apps you cant have that) then you should just keep the operating voltage lower than the normal operating voltage. That will reduce the temperature but will still prevent fire.
The coils are made out of NiChrome wire and that can take a lot of abuse, but it wont last forever if it is heated to a higher temperature than normal.
Just to note, they do make immersion heaters made to be put into liquids to heat them up. They MUST be under the liquid though or they could burn up too. Not sure how much heating power you need either, 100 watts, 200 watts, 1000 watts, etc.