The measure command has potential for a solution but it presents two challenges to be fully automated from a list of commands generated by Excel.
1. Measure may create more than one instance of the block. The length specified will be used to create as many blocks as necessary to fill the length of the polyline. You would need to manually delete all but the first instance.
2. The measure command prompts the user to "Select object to measure:". The command will not accept a "p" (previous) nor a "g" (for group) at this point. It will accept a vlisp point name variable so vlisp could be used to select the polyline for subsequent blocks but I have encountered a problem with this approach.
The attached Excel file uses the concatenate command to build vlisp statements. It uses char(34) to generate quote marks that are need in the vlisp statement as opposed to quote marks needed for the concatenate function.
Before using the commands you must define a point on the polyline. This can be done with the command (using osnap nearest):
(setq pt (getpoint "\nSpecify point on the polyline"))
Copying and pasting column C into the AutoCAD command line or creating a script produces the same result. Only the first line gets successfully executed. Not sure why.

The full contents of cell C2 is:
=CONCATENATE("(command ",CHAR(34),"_measure",CHAR(34)," pt ",CHAR(34),"b",CHAR(34)," ", CHAR(34),A2,CHAR(34)," ",CHAR(34),"Y",CHAR(34)," ",B2," ",CHAR(34),CHAR(34),")")
Here are the results. As noted, only the first execution is successful.

Attached are the files I used .
lee.minardi