Delta Gift Card Workaround

So I bought about $2K of Delta gift cards during the "buy $300 of Delta GC, get $25 Starbucks GC free" only to just now find out that Delta GCs have a million and one restrictions - can't use for upgrades, can't pay for the cash portion of miles+cash, etc.

I have seen threads where people who have multiple GCs buy a refundable ticket, cancel it, and it is credited as a eCredit, which does not appear to have as many restrictions - please correct me if I am wrong!

Would it make sense for me to purchase and cancel a refundable ticket, get an eCredit, and use that towards paying the cash portion of my miles+cash ticket?

In case anyone wanted to know why want to do this....I have 118000 Skymiles and $1800 in GCs. Looking to buy 2 tickets that are $2176 cash a piece for premium. Saw that main is going for 59000 miles + $325 per ticket. Want to find a way to use my miles to buy 2 tickets and the GCs to upgrade the seating.

Thanks for any and all advice!