I do trace metal shore side sampling in shallow estuaries and have a similar problem. The best solution I have found is simply a 3 m long wood/plastic pole that was made in our workshop. The last meter entirely consists of plastic, with a snug holder for 500 ml LDPE bottles at the very end such that bottles can be submerged and emptied a few times away from the shore side before collecting water.
Mark, do you wait with the filtration until you get back to your lab? I can't do the filtration on the same day, so looking for clean filtration setting as well.
We have some hand pumps that we carry into the field with a plastic mounted filtration unit. It's a little tricky as everything has to be acid cleaned, bagged and carried into the field, but its better than leaving the water samples for several hours before filtration.
Buy a telescoping paint roller extension and bolt a clamp to the end. You can add dense foam to the clamp in order to better fit your sampling vessel. This will allow you to sample from shore.