The download can be found here https://github.com/BOLL7708/OpenVR2Key/releases
A video tutorial here https://www.youtube.com/watch?v=f9ZOBYzTpUQ
This application basically allows you to bind your VR controls to keys on your keyboard. This is necessary because you cannot bind your vr inputs to the source engine. Once you have chosen a button from your controllers and bound it to a key, note that you might want to change that button in the controls for HL2VR so they aren't overlapping.

After getting OpenVR2Key setup, you'll need to enter the proper code into source in-game.
Once loaded into the game press the tilde key to pause and open the console.
Then input the following code -bind x "incrementval host_timescale .1 1 .8"-
Everything between the dashes. x will be the key you have bound your chosen control to in OpenVR2Key. Then .1 will be the lowest modifier followed by 1 the highest modifier followed by .8 the change between the two. Note .9 will not work as it is the absolute difference between .1 and 1
Experiment with these numbers, for example. bind x "incrementval host_timescale .3 1 .6" will give you a faster rate of time when activated. bind x "incrementval host_timescale .5 1.5 .9" will give you a variation between half rate and one and a half rate.
Don't forget to set sv_cheats 1