First of all, if you truely only have one single public IP this isn't going to work trying to port forward the same port for two internal hosts.
If though you have a range of IPs, perhaps your ISP has given you a small /29 subnet, then you are in luck. If they are routing a /29 to your ASA then obviously as usual, you can only configure one IP on the outside interface but if it is receiving traffic for those additional IPs it can work with them.
(The below is an example from an ASA that gets assigned an IP over PPPoE and the ISP routes a /29 to that interface, but if for example your uplink is an Ethernet segment, ASAs can use proxy ARP).
As you haven't given the version of ASA OS you are running I can't more specific, so here is an example I have use, which is on 8.2. This is allowing RDP (port 3389) on a second public IP in the same subnet routed to the ASA, two a second internal hosts (I have included the default NAT rules etc so you can see the bigger picture).
! Assume we get assigned the public IP 184.108.40.206, and also in this subnet
! routed to the ASA is 220.127.116.11
! RDP to 18.104.22.168 goes to 2nd internal host 192.168.0.20.
pppoe client vpdn group PNDSL
ip address pppoe setroute
switchport access vlan 2
access-list inside_access_in extended permit ip any any
access-list outside_access_out extended permit ip any any
access-list rdp_inbound extended permit tcp any interface outside eq 3389
access-list rdp_inbound_54 extended permit tcp any host 22.214.171.124 eq 3389 log
global (outside) 1 interface
global (outside) 2 126.96.36.199
nat (inside) 0 access-list inside_nat0_outbound
nat (inside) 1 0.0.0.0 0.0.0.0
static (inside,outside) 188.8.131.52 192.168.0.20 netmask 255.255.255.255
access-group inside_access_in in interface inside
access-group rdp_inbound_54 in interface outside
access-group outside_access_out out interface outside
I hope this is the correct config for you, been focusing on 8.4 as the changes they have introduced are too much for my simple brain and pre-8.4 stuff is falling out of my nose!