According to the specs, the warp and fill break at 122 and 106 lbs respectively. Warp being fibers that run the length of the spool and fill being fibers that run raw edge to raw edge of the bolt of material.

While you have many fibers over which to spread the weight, it still means that to keep from destroying the poncho, you at least want to double the poncho over for any hope of avoiding any realized destruction to the poncho. It will give you an area roughly 9 feet long by 2.5 feet wide.

The next consideration is the grommets/anchor points. Any anchor point will have exponentially increased stress at that point. Grommets are out. I wouldn't consider web loops either on such a thin fabric due to the seam slippage of the material....which based on the specs is less than half of the tensile strength of the fibers.

Seam slippage is what happens when sufficient stress for the fabric is applied and the fibers near the seam (or any area joined by sewing) begin separating.

The best method of anchoring would be to wrap the material around a smooth (or intentionally smoothed), round log, pole or stick in order to spread out the stress along the material. At that point, ANY type of grommet or anchor could be used as a means to ensure against the wrap slipping out, by means of staking/tying, as long as the chosen method had no danger of compromise of fabric it happened to come in contact with.