You don't need a steak knife to cut steak, almost any knife will do, and thats the idea behind using adapters to force a gpu to work on psu's not designed for that purpose.
But what you want to attempt is similar to cutting a steak with one of those plastic butter knives you get at picnics.
In theory, 700w is far more than necessary, but in reality the insides of that psu are not designed for a gaming gpu, of any sort, and the manufacturer knows this, so it didn't include the necessary connectors.
Sorry, but you'll need a real knife for this job, the plastic one isn't going to cut it.