I think if you explained what you were going to do with the taxpayer, explain to them that you were going to provide the bankruptcy attorney with copies, and then execute a simple one page authorization putting that agreement/waiver in writing that includes the IRC 7216 disclosure and consent language, you should be OK.
A couple of issues:
1. I assume that you are going to charge for this service, correct? Where I see a small flaw is: For example, if you list the BK atty as the POA, it takes you out of the service you are attempting to provide, no? i.e. with the POA, the BK attorney can order it themselves. I am sure your business model is predicated on your being able to deliver it much faster, but a BK attorney who otherwise knows about the tax world can use that to just ice you out of the process.
2. Also, a full blown 2848 POA implies a lot of other responsibilities that the BK attorney would probably not want to deal with, and in many cases, may not even be aware of. So, depending on the level of tax knowledge the particular BK attorney has, there may be a duty to disclose on your part on what the responsibilities in signing a 2848 POA imply.
3. depending on the scope of your representation, have you considered an 8821 representation instead vs a full blown 2848 POA?