I swear I posted but don't see it. If this turns out to be a dup, ignore.
The following is a ramble. Sorry, big and complex topic and I like to pontificate. I am the sole admin/dev at my company and we have to deal with these types of issues.
What problem does security want to solve? What's the risk associated with the problem? How many ways can you mitigate the risks? Open a conversation with your security folks and get to the root of their concern.
If there are two of you and you're both devs and admins, then anything you do to try and segregate roles is security theater; both of you can do everything. Unless you staff up or turn one of you into a full time dev and one a full time admin, doing things like playing with roles or switching ID's is just playing 'hide the banana'.
Do you have a good backup system so if the two of you go rogue, the business can recover quickly? Is the backup system managed by someone not you? If it's you, then there is nothing the business can do short of hiring new staff to address that level of risk.
Is there a concern about the two of you adulterating records? Get AuditManager from OpenNTF and set up audit trails. Then again, since you're both gods of the empire, you can muck with the audit system also...
What's the risk if you do split roles? If there's one admin and one dev, what happens when one of you isn't available? Is the loss of business continuity a problem?
Do you have good change control? If so, it should be the source for proof that you're following a process. Security can audit to see if <change> was implemented after change approval (look at time stamps on design elements or docs for instance).
Did either of you bork something and spawn this discussion? How can the problem be prevented?
With small staff wearing multiple hats, the business has to accept some risk associated with 'security'. If you aren't going out of your way to do bad things...perhaps the security staff needs to calm down!
Hope this helps.