There is no way around this, the remove admin privelages is set in stone at least I hope it is..
If its not, then we are basically producing open source runtime files...
Work around :
Copy the runtime file to your machine and import the data into a copy of your development file
make the changes and re-import the data back to their system.
What we do (something to consider for future)
We also have a maintenance file, which is not distributed to the end user.
This is linked to our main distributed files by having them as data sources and is bound to the runtime.
The maintenance file contains Table Occurences and layouts of all the base tables, with all the fields in place, and a few scripted buttons to allow us to run pre-set functions from the runtime files.
In case of such problems, we transfer the maintenance file, open it and hey presto.. can manipulate the data in any way required since we have full access to all the tables, fields and menu commands available in a runtime such as importing and exporting, replace all etc etc.
Thinking about it, you could build the maintenance file now it shouldnt take long to make a crude looking file, linking it to the main db using your dev copy, bind it to a runtime using the exact same details as previously used, then send that one bound runtime file over to your clients machine.. open the solution, then open the maintenance file, this will then allow you to access the data. When your done, you can simply delete it or leave it in place.