Maybe enumerate the possible default gateways and see if your preferred one is in the list...
Code:

Dim $arrGateways[]
$arrGateways = EnumGateways()

;Dim $strGateway
;For Each $strGateway In $arrGateways
; $strGateway?
;Next

If AScan($arrGateways, "192.168.234.1") = 1
Use p: "\\MyComputer\Share\Deeper"
EndIf

Function EnumGateways()
Dim $Count
$Count = 0
Dim $Junk
Dim $arrGWInfos[]
While NOT @ERROR
$Junk = EnumIPInfo($Count)
If NOT @ERROR
ReDim PRESERVE $arrGWInfos[$Count]
$arrGWInfos[$Count] = EnumIPInfo($Count, 3)
$Count = $Count + 1
EndIf
Loop
$EnumGateways = $arrGWInfos
Exit 0
EndFunction