Digital signatures on a repeating field

[rmuti]

I'm building a workflow solution using InfoPath and I could use some advice.
I've searched everywhere, but I can't find a workaround to this problem.

I have a form that can be approved by a series of approvers. The number of
approvers is not known at design time. Approvers can be added dynamically
after the workflow has been initiated. I want each approver to have a
section on the form to enter their name, decision (approve, reject, or
request more information), and any comments. I also need them to digitally
sign this section for identity verification purposes. This will create an
audit trail within the form. Since approvers can be added dynamically, I
would normally create these approval sections as a repeating group. However,
there doesn't seem to be any way to support digital signatures on individual
instances of a repeating group (if you sign one, they all get signed).

I can understand why this doesn't work as desired (the set of signable data
is bound to an XPath expression, which matches all the instances of the
repeating group), but there must be some half-decent workaround for this.
Any advice?

Thanks in advance.