Unless you are doing a coupled approach in which case you will never get GS capture.
I think intercepting the GS from above is dodgy.
If you are really sure you are just above the GS, you can uncouple the autopilot and push the yoke down hard and hope to get an intercept and then fly it by hand, or even re-engage the AP, but it is a bit tacky.
I have been vectored above the GS a few times; the last time was Bournemouth. But to be fair it could have been avoided by me doing a really rapid (-1000fpm or faster) descent to the platform.