Adding Custom Properties to Signature Field

Hello-

Using Acrobat Pro and have added an acro form digital signature field to a PDF.  I'm working with a provider that requires that I add several custom properties to the field for additional parameters that they must receive, read, and apply as part of the signature path within their signing tool. 

I do not see anywhere within the UI to add a custom property, so I started digging into field tags and believe this is where I can add the property, but I'm not sure which key/value/value types to apply to add the properties to the field.

The output of the form field would look something like this prior to adding custom properties: 

2 0 obj <</MK<</BC[0 0 0]/BG[1 1 1]>>/F 4/Type/Annot/Border[0 0 0]/Subtype/Widget/Rect[20 37 209 70]/SignerName(Signer)/FT/Sig/DR<<>>/T(Signature in Box 15)/AP<</N 1 0 R>>/P 3 0 R>> endobj,

I need to add the custom properties to the field, which would make the output look something like this (see ESHPROP references):  

75 0 obj <</ESHPROPrequired(true)/F 4/Type/Annot/Border[0 0 0]/ESHPROPtype(sig)/Subtype/Widget/SignerName(Signer)/DR<<>>/T(Signature in Box 15)/AP<</N 74 0 R>>/P 21 0 R/ESHPROPlabel(Signature in Box 15)/MK<</BC[0 0 0]/BG[1 1 1]>>/Rect[20 37 209 70]/FT/Sig/ESHPROProle(Signer)>> endobj    

Any idea what I need to do to get these custom properties into the field so the receiving API/service can read it?

Screenshot of the tag UI where I think I can add these custom properties attached.

Help appreciated!Image may be NSFW.
Clik here to view.