I actually have the velcro strips that are designed to loop back through themselves to wrap around cables so that they won't get lost, when not fully wrapped around cables. I am thinking I can use those to loop around the mask, or to connect to each other. I will experiment to see which way is more comfortable.
I also use a F-P Simplus, and had/still have a bit of the mask sliding up toward my eyes problem. I have modified the upper straps so that they dond pull the mask up so much, and have used Moleskin to interface between the mask's silicone plastic and my face. This has allowed me to loosen the straps considerably. Also, I cut off the "across the top of my head" strap completely so that the upper straps only pull the mask around my head and not up.
If you are interested in some of the other modifications I made to get a good comfortable seal, email me, and I'll send you back some pictures and a description.
PS: I have been using, and trying to get a comfortable fit out of CPAP/BiPAP nasal and full face masks for over 20 years!
Having the same problem and early days for me but I am having a bit of success using something my wife made modeled on the pada cheek anti leak strap.
I tried the Velcro strap under the chin but it did not work well for me. I will try again but the strap I mentioned seems to work ok
One thing I did find is that you have to be careful with the Velcro strap, they make a mess of the mask straps if they keep getting attached to it.