access rb with public ip with other gateway

Hello all, i want help to solve a problem i have…

One of my routerboards connects to my network.
ip: 10.10.248.5
gw: 10.10.248.1

I have also give a static ip to this routerboard with pptp connection to my main vpn server.

What i want is: my routerboard to keep the default gateway 10.10.248.1 but i want to be able to access it with it’s public ip too.

If i have default gateway 10.10.248.1 i can NOT access from it’s public ip
but if i make default gateway the pptp connection (public ip) then i can access it.

How can i do this?
Keep gateway 10.10.248.1 and also access it from the public ip???

anyone???