Private record line for conference calls

I have a need to record cell phone calls when a USER in the field make or receive certain phone calls.
One thought was to setup a phone number the USER could conference in on their phone that would strictly automatically answer and record the line.
For example, the USER receives a call on their cell. If they need to record it they tell the caller “just a moment”, then use the “Add Call” feature on their iPhone to dial the special phone number on our FreePBX. The PBX answers the phone automatically, and keeps an open and quiet recorded line. The USER then selects “merge call”, and the original caller, plus the recorded line, are all conference together.
Similarly, if the USER wants to make a call, they do the same but first call the special # with the recorded line, then “Add call”, dial the person they want to speak with, and “merge Calls”.

I would need to be able to have multiple cell USERs (5?) do this at the same time.

I already have the special number, and trunk setup and inbound route. Now what is next to make the above work?

Does the FreePBX “record on demand” (which uses asterisk’s “one touch record”) feature not work for you?

Thanks for the suggestion.
Keep in mind these calls to record are received or begin from a cell phone. How do you see the one touch record fitting into that scenario?

That wasn’t clear to me, maybe send the call to an extension that answers your call and then dials your “dictation” feature code.

It might be easier to just have the guy in the field call into a trunk that links him to a DISA. DISA allows him to get a dial tone and dial out from the system. You could enable call recording for all such calls.

Just be sure to set a secure password for the DISA…