The only way to relieve the pressure on a leaking well (until the relief well is finished) is to tap the oil. There is no way to simply "block" the oil, it will just leak out.
Nuke it. srsly
The relief well is just another well. I don’t think it will relieve the pressure substantially. Saudi Arabia is full of wells where the oil flows up and is collected using the pressure of the field. The fact there are lots of holes and wells doesn’t mean one will cease to flow when another is opened.
Eventually the pressure might be lessened but not in the immediate future.