YES you can
/ip firewall mangle
add action=mark-connection chain=prerouting comment=\
"Mark every 2. new connection for pppoe-out1" connection-state=new disabled=no \
in-interface=ether1 new-connection-mark=pppoe-out1 nth=2,1 passthrough=yes
add action=mark-routing chain=prerouting comment=\
"Mark all packets in conn pppoe-out1 with routing mark pppoe-out1" \
connection-mark=pppoe-out1 disabled=no in-interface=ether1 \
new-routing-mark=pppoe-out1 passthrough=no
add action=mark-connection chain=prerouting comment=\
"Mark the rest of new connections for pppoe-out2" connection-state=new \
disabled=no in-interface=ether1 new-connection-mark=pppoe-out2 nth=2,2 \
passthrough=yes
add action=mark-routing chain=prerouting comment=\
"Mark all packets in conn pppoe-out2 with routing mark pppoe-out2" \
connection-mark=pppoe-out2 disabled=no in-interface=ether1 \
new-routing-mark=pppoe-out2 passthrough=no
just add more pppoe-out3 and out4
/ip route
0 A S 0.0.0.0/0 pppoe-out2 1
1 A S 0.0.0.0/0 pppoe-out1 1
2 A S 0.0.0.0/0 pppoe-out1 2
3 S 0.0.0.0/0 pppoe-out2 2
4 ADC 192.168.1.0/24 192.168.1.1 ether1 0
just add pppoe-out3 and 4 to route
/ip firewall nat
3 ;;; Masquerade interfaces
chain=srcnat action=masquerade out-interface=pppoe-out1
4 chain=srcnat action=masquerade out-interface=pppoe-out2
just add pppoe-out 3 and 4 to nat
and .... it should work
Njoy