My first observation, is that you have 3 capabilities. Are you trying to ask how to escalate your capability set to all capabilities by becoming root? At first glance it seems like you are trying to gain all capabilities (by becoming root) while having only 3.
Second observation is that you don't specify what the system's capability is bounding set is. I.e. if the overall bounding set is only those 3 capabilities, then becoming root will have no effect.
Third observation is that you don't specify what the "securebits" are. Depending on their value it may be impossible to add any further capabilities or it may be the case that becoming root does nothing more than change your UID (i.e. root is no longer special).
Fourth observation -- while you are starting your bash shell with the listed capabilities, you don't show that bash has actually retained those capabilities. You might want to make sure.
But I'll go with observation #1 and say that what you are asking shouldn't be possible. If it is, it seems like it would be a kernel security bug -- specifically a privilege escalation. If you do find a way to do it, I would think it wouldn't stay around long, as security bugs are usually fixed ASAP.
Am I missing something in your use-case as to why this wouldn't be a security bug?