You can use form 2848 to appoint an agent for the sole purpose of signing a return, if due to disease or injury. That agent does not need to be a representative that is qualified to practice before the IRS. The instructions on page 5 of the instructions explain how to do this, but they aren't very clear. They indicate:
To authorize an agent who is not your representative, you must do all four of the following:
1. Complete lines 1-3.
2. Check the box on line 4.
3. Check the box on line 5a titled “Sign a return” and write the following statement on the lines provided:
“This power of attorney is being filed pursuant to 26 CFR 1.6012-1(a)(5), which requires a power of attorney to be attached to a return if a return is signed by an agent by reason of disease or injury. No other acts on behalf of the taxpayer are authorized.”
4. Sign and date the form. If your agent e-files your return, he or she should attach Form 2848 to Form 8453, U.S. Individual Income Tax Transmittal for an IRS e-file Return, and mail it to the address listed in the instructions for Form 8453. If your agent files a paper return, he or she should attach Form 2848 to your return. See Line 7. Signature of Taxpayer, later, for more information on signatures. The agent does not complete Part II of Form 2848
For an agent that is not a representative, it is not clear, but I would probably still complete line 2 with the agent's relevant information (since you need to identify the agent somewhere) and leave off any information that is irrelevant, such as CAF and PTIN. Line 3, again it is not clear, but I would probably simply say "sign a return (see line 5(a)) below)", include the Tax Form number and Year(s) (since you need to identify the relevant form and year for which signing is authorized). Then follow all of the other instructions above with respect to attaching appropriate forms if e-filing or mailing and signing.
