On the topic of many x16 cards being used in x1 slots. Yes is "Should work" Many have done it. Great way to get an extra screen or 2 if needed
Many have even cut the card if it gets in the way of other board components.
I see no reason for the riser to not work.
Want to be sure it will work?
Tape off the extra connectors on the card just like toms did here. I know your card is only an X4 but as long as you leave the same pins showing, you should be good to test x1. Please ensure the tape is tight and passes the connector so it does not get stuck.http://www.tomshardware.com/reviews/pci-express-scaling-analysis,1572-4.html
Once taped, place the card in the X16 slot. If it works, then you should have no issues.