That would be a bad idea. The topic hasn't come up for over a year - but the PS90 floats free, and moves while firing. In the past, we have discussed that when using FN's sling that attaches directly to the barrel, one should not put pressure on the barrel when actually firing it.
There is a possibility of damaging your receiver over time by mounting that much weight, that far forward. I wouldn't do it if it were me