You could make different INIs for B4A and then use a startscript (or tool) which copy the right INI to
C:\Users\{username}\AppData\Roaming\Anywhere Software\Basic4android\b4aV0.1.ini
and then start B4A....
In this ini you find the informations which key is used.
As i wrote: you COULD. But i suggest to not doing that... The time will come and you work with the WRONG B4A-INI and then your problems are big.
As Erel says: In most cases there is no need for different Developer keys. I personally know NO case.
BTW:
IDE doesnt remember different private key assigned to each app
It´s not a bug; It´s a feature! It remembers THE selected sign-key
You dont have to be worry about the damned signkey. You set it up once and you´re gone. No need to change it.