Hey Tim,
What you can do is assign foot switch(Global 6. Foot Function) = Arp Hold.
Then use MIDI to trigger the foot switch function with
CC64 = 127 for on
CC64 = 0 for off.
How I learned this..
Set up your footswitch to Hold Arp. test it with your foot switch. Play a chord and press pedal = HOLD.
My footswitch (Korg PS-1) will momentarily engage HOLD while foot switch is pressed and ends HOLD when foot switch is released.
I recorded a short MIDI clip in Reaper - and on MIDI play back the T5 will play the chord and hold it for the duration of CC64=127 until CC64 =0
Of course, if you set Global 6 Foot Function to something other than ARP Hold, like Sustain, Seq Start/Stop then those functions will play when CC64 =127
Global 6 Foot Function has ARP Hold, and ARP Hold Mom, but they both work momentarily for me.