I researched the issue of Pick-up contributions in Maryland several years ago, and this was my answer then:
The way it works is that after you have entered Maryland as your state of residence, then you enter the 1099-R. In the interview following the data entry of the 1099-R, you will be asked if part of this is your state pickup. If so, then you are asked how much of it is the pickup. As best as I can tell, it doesn't matter if anything is in boxes 16 or 19, this amount entered in the 1009-R interview will carry to the 502SU.
NOTE: if there is only 1 subtraction on the 502SU, then in accordance with the Maryland instructions, form 502SU is left off the return, and the "R" and dollar amount are put on line 13 on the 502.
NOTENOTE: I have done this on the desktop product; are you using the Online product? I will have to check there next...
Let me know if this works for you or not.