problem with hotspot users authenication

Dears
good evening to all
i have one problem with this scenario below:
i get internet from A-ISP with hotspot users authenication via Wireless , i am also want to be ISP for others , i used RouterBOARD 951G with configure hotspot users authenication, every thing working very well , but the problem is when the internet of A-ISP is down and come back again , the hotspot main page of A-ISP will apper to my customers unless pass my authenication methods in A-ISP
how to hide the hotspot main page of A-ISP for my customers?

note: also A-ISP using RouterBOARD 951G to provide us the internet

I think you’re not able to bypass it from your RB951.
You can either ask your ISP to bypass your mac-address on his hostpot or set up a linux server and write some scripts to input the credentials automatically.

I was also facing similar problem few days back may be due to slow server. But I like your answer jacekes. I opt to set up a linux server to resolve the issue.