Replace Placeholder Text

I have a spreadsheet that I receive from my customer containing business requirements. One such requirement is a string of text that sometimes contains variable(s) represented by placeholders. I need to copy this string into another worksheet and replace the placeholders with my internal variables. This will allow for a straight comparison during QA.

Worksheet 1
Cell A1
Lorem ipsum [!--$VARBL1_TXT$--] sit amet [!--$VARBL2_TXT$--]

Worksheet 2
Cell A1
Lorem ipsum %%Variable1%% sit amet %%Varaiable2%%

I am currently copying W1/A1 into W2/A1 using this formula: =IF('W1'!A1="","",'W1"!A1)

I do have a table that I can use for a VLOOKUP but the logic to return both the W1/A1 with replaced values has me baffled. I have written this macro but it doesn't work on the cell value returned from the formula in W2/A1:

Sub abbrev()

Dim advtab() As Variant
Dim ltsheet As Worksheet
Dim datasheet As Worksheet
Dim lt As Range

Set ltsheet = Sheets("W3LookupTable") 

Set datasheet = Sheets("W2")

Set lt = ltsheet.Range("A2", ltsheet.Range("B2").End(xlDown)) 

advtab = lt

For i = 1 To UBound(advtab)
    datasheet.Cells.Replace What:=advtab(i, 1), Replacement:=advtab(i, 2), LookAt:=xlPart, _
        SearchOrder:=xlByRows, MatchCase:=True, SearchFormat:=False, _
        ReplaceFormat:=False

Next i 

End Sub

What is the best way to manage this? I considered doing nested substitutes but there are apx 30 variables. Thanks in advance!